Settings: Add availability information to the list of variables

[Taitava]

This is the current view of {{variable}} listing in settings:

Make the listing to be a <table> that contains a new column: Availability. Edit: Just continue using paragraphs, but add a new row to all variables that are not always available. This will indicate situations where a particular variable can or cannot be used, e.g. if a file needs to be active in Obsidian.

123 will also add event related variables, so the related events will also be mentioned in the new column.

[Taitava]

• [x] Also add the availability information to autocomplete menu.
• [x] Update Documentantion by adding an Availability heading to all variable pages.
• Everything else is done.

[Taitava]

Done.

[Taitava]

Just for the record, here is a preview of the new availability texts. Not all of them fitted in the picture.