Apprise: support for stateful api call

[Splinter7914]

https://github.com/caronc/apprise-api#persistent-stateful-storage-solution

Using this one could make calls such as

http://apprise-api:8000/notify/abc123

With this we could avoid having to specify notify url's option and let the user control that in apprise.

Wondering if we can add support for it?

[alexlebens]

I use APPRISE_STATELESS_URLS which is another way to not require the notify url option. That option should not be required. Maybe an option to enable send without url?