Log warnings/errors on unrecognized plugins

[Xeverous]

Requested Feature: Avoid silent warnings on unknown/misconfigured plugins.

Related Area: .plugin files

Do you want to contribute this yourself as a pull request? (don’t worry about it if you don’t want to/can’t — someone else can take care of it)

• Yes, I have already written code for it (link if available and feasible)
• Yes, I don’t have code ready yet (that’s okay!)
• No (that’s okay too!)

Does this feature affect backwards compatibility? If yes, in what way? No.

Rationale and full description: (why should it be added to Nikola?)

Recently I updated my Nikola version from 8.2.3 to 8.3.3 and noticed some of my plugins do not load (as if the files did not exist). Turned out there were 2 very small breaking changes:

First, from v8.0:

Nikola now requires the .plugin file to contain a [Nikola]
section with a PluginCategory entry set to the name of the plugin
category class. This was already required by plugins.getnikola.com,
but you may have custom plugins that don’t have this set.

Second (unannounced) I had to edit my .plugin files from this:

[Nikola]
PluginCategory = RestExtension

to this:

[Nikola]
compiler = rest
PluginCategory = CompilerExtension

https://getnikola.com/extending.html#restextension-plugins links to media.py which was correctly updated. It was just surprising for me to have my plugins fail completely silently, even when [Nikola] was present but with older categorization naming.

Feature: make this some kind of error. If a plugin can not be loaded or has unrecognized fields in the [Nikola] section it should be visible in logs when building the website.