Added event id to simpleCalendarEvent
SimpleCalendarEvent:
-added event id field

SelectCalendarsActivity:
-maybe fixed the checkboxes showing on the wrong calendar (untested)

DatabaseInterface:
-promoted EventDatabaseOpenHelper to top level class
-moved some private members to EventDatabaseOpenHelper

build.gradle:
-added lint option not to abort building on ling error, this should help with travis integration later