Removed duplication in Sidebar
Fixup CalendarsController: Simplify start_date determination

Calendars Controller refactored with @railsbros-dirk
Better Solution
Suggest Events moved into the day divider

It doesn't have the icon from the draft yet, because it is not here
yet.
Cleaned up the lib directory

Thanks to @railsbros-dirk

* Calendar and Day are in Models now
* CalendarEntry, StartSelector are in Presenters now
* DatetimeParser is not used and therefore deleted
* Useless form scaffold removed
* Adjusted the specs accordingly
Introducing spec_without_rails_helper