adds individual "enabled" prefs for each calendar (Solstices/Equinoxes, Moon Phases) (#3).
fixes bug "missing calendars/events when closing app while task is still running" (#4); moves calendar notifications into a foreground service.
changes the "Calendar Integration" pref to match calendar state (vs desired state); existing calendars (and prefs) should be preserved when updating (or removing / re-adding) the app.
changes the strategy used when initializing calendars; existing calendars are no longer cleared prior to (re)adding; subsequent calls to "add" instead "update" a calendar (insert, replace).
changes when permissions are requested; adds a request on first launch (or if data is cleared) before allowing access to remaining UI; permissions are used to recover calendars from previous installations.
misc improvements to permissions handling; more robust; support for actions on individual calendars.