Stripping local database to minimum values

Columns:
-local database now only stores the:
  -instance id
  -event id
  -calendar id
  -ringer type

EventDatabaseOpenHelper:
-bumped up version number to 7
-changed database creation to only use the minimum values from Columns
Fixed possible bug in EventInstance
-changed all ids to longs to avoid any potential loss of precision errors
NOT WORKING reducing resource useage in database interface
Refactoring

Prefs:
-renamed getSelectedCalendars() to getSelectedCalendarIds()

EventDetailsFragment:
-changed constructor to take long value for instanceId
Adding icons
-added icon for tutorial (question.png) (fixes #29)
-replaced history_icon.png with a higher quality version, renamed to history.png, will be used for repeating events (fixes #26)
-replaced clock.png with a higher quality version
 -added code.png to replace the use of history_icon.png as the changelog icon