Add compatability with new periodic notes plugin

[burgerga]

Got started on this to have compatibility with the new Periodic Notes plugin, but turned out to be a little more work than anticipated :)

I think we're mostly there:

• Refactored settings.ts and and index.ts to be compatible with both 0.0.17 and >=1.0.0 (I have tried to keep the exported functions the same, but ended up changing shouldUsePeriodicNotesSettings to shouldUsePeriodicNotesPluginSettings, as the argument changed from string to IGranularity, so major version number should be bumped)
• Just discovered there is quite a bit of settings stuff in utils.ts as well
• tests and mocks

I have little experience with mocking interfaces, some input from you would probably be needed here.

In it's current form this pull request already fixes #24 (have tested with day planner using both legacy and new periodic notes plugin versions), but for full compatibility the other aspects should be fixed as well.

Might also solve liamcain/obsidian-calendar-plugin#307 but haven't tested, input from that side welcome as well :)