Markdown linting: Fix MD001 errors and enable rule (#5561)

* MAGEDOC-5240: enabled MD001 header increment rule

* MAGEDOC-5240: additional fixes

* Added a new class for fake headers so we can implement MD001

* Added new devdocs class for pseudo headers

* Replaced all reference headers with pseudo header class

* Fix global replace error

* Fixed more global replace issues

* More fixes and replace NExt steps in cloud

* Add new line

* Peer review edits

* Add class to Previous step

* Fixed MD012 error

* Changed long H3s to bullets

* Fix MD001 error after fixing merge conflicts

Author: jeff-matthews

_checks/styles/style-rules-prod

@@ -1,4 +1,4 @@
-exclude_rule 'MD001'
+rule 'MD001'
 exclude_rule 'MD002'
 rule 'MD003', :style => :atx
 exclude_rule 'MD004'

_includes/install/web/install-web_4-customize-store.md

@@ -17,7 +17,7 @@
 
 1.  Click **Next**.
 
-#### General module configuration options   {#instgde-install-magento-web-step4-depend1}
+### General module configuration options   {#instgde-install-magento-web-step4-depend1}
 
 Modules are listed in **Advanced Modules Configuration** in alphabetical order; the order has nothing to do with dependencies.
 
@@ -37,7 +37,7 @@ The following figure shows an example of disabling the `Magento_GoogleAnalytics`
 
 ![Disabling a module]({{ site.baseurl }}/common/images/install_wizard_disable-google.png)
 
-#### Module dependency errors   {#instgde-install-magento-web-step4-depend2}
+### Module dependency errors   {#instgde-install-magento-web-step4-depend2}
 
 A dependency error occurs when two inter-dependent modules are disabled at the same time.
 

_videos/fundamentals/create-a-new-module.md

@@ -21,11 +21,11 @@ Let’s go through each of these steps in detail.
 
 ## Create the module folder
 
-#### There are two possible locations for modules in Magento 2: the app/code folder and the vendor folder
+### There are two possible locations for modules in Magento 2: the app/code folder and the vendor folder
 
 Depending on how Magento 2 has been installed, core modules can either be located in the `vendor/magento/magento-*`folders (for composer installation) or in the `app/code/Magento/` folder (for cloning GitHub).
 
-#### Which of these locations should you choose for your new module?
+### Which of these locations should you choose for your new module?
 
 If you build a module for a specific project, it is best to choose the app/code folder and commit to the project's repository.
 

_videos/fundamentals/create-a-new-page.md

@@ -49,7 +49,7 @@ Learning/HelloPage/registration.php
 Learning/HelloPage/etc/module.xml
 ```
 
-#### registration.php
+### registration.php
 ```php
 <?php /**
 * Copyright © 2016 Magento. All rights reserved. * See COPYING.txt for license details.
@@ -59,7 +59,7 @@ __DIR__
 );
 ```
 
-#### module.xml
+### module.xml
 ```xml
 <?xml version="1.0"?>
 <!--

common/css/devdocs.css

@@ -28,6 +28,13 @@
   margin-left: 1.0em;
 }
 
+/* Paragraph that introduces important reference information (e.g., Related topics, Next step, Previous step), but does not qualify as a proper heading. Mimics the current H3 style */
+.ref-header {
+  font-weight: bold;
+  font-size: 1.3em;
+  margin: 1.5em 0 0.5em 0;
+}
+
 .message-banner.version-banner {
   margin-bottom: 15px;
 }

guides/v2.2/advanced-reporting/data-collection.md

@@ -196,7 +196,8 @@ It cannot contain any parameters.
 ...
 ```
 
-## Related topics
+{:.ref-header}
+Related topics
 
  [Modules providing advanced reporting][modules]
 

guides/v2.2/advanced-reporting/overview.md

@@ -30,7 +30,8 @@ To avoid system overload during its prime time, you can set the preferable time
 
 Though the Analytics module provides API, it is used specifically to interchange data with the MBI. We do not recommend to extend the advanced reporting functionality in this version.
 
-## Related topics
+{:.ref-header}
+Related topics
 
 [Magento modules that implement the functionality][modules]{:target="_blank"}
 

guides/v2.2/architecture/archi_perspectives/ABasics_intro.md

@@ -15,7 +15,8 @@ The following discussion focuses on how these topics apply directly to Magento:
 * Event-driven architecture
 * Security
 
-## Related topics
+{:.ref-header}
+Related topics
 
 [Architectural diagrams]({{page.baseurl}}/architecture/archi_perspectives/arch_diagrams.html)
 

guides/v2.2/architecture/archi_perspectives/ALayers_intro.md

@@ -22,7 +22,8 @@ Layered application design offers many advantages, but users of Magento will app
 
 * Clear organization of code predictably points [extension](https://glossary.magento.com/extension) developers to code location.
 
-## Related topics
+{:.ref-header}
+Related topics
 
 [Architectural diagrams]({{page.baseurl}}/architecture/archi_perspectives/arch_diagrams.html)
 

guides/v2.2/architecture/archi_perspectives/arch_diagrams.md

@@ -14,6 +14,7 @@ The following diagram illustrates the components and shows the "layers" or tiers
 
 ![Architectural Diagram]({{site.baseurl}}/common/images/archi_diagram_desired-state.png)
 
-## Related topics
+{:.ref-header}
+Related topics
 
 *  [Architecture layers overview]({{page.baseurl}}/architecture/archi_perspectives/ALayers_intro.html)