added ability to use Countly without CoreData, and run it on a single background thread
replaced [CountlyDb sharedInstance] singleton with an object owned by the [Countly sharedInstance] singleton
added protocol for CountlyDB and ability to use a different CountlyDB class
added ifdefs with COUNTLY_COREDATA_DISABLED to prevent compilation of CoreData stuff

*	modified:   Countly.h
*	modified:   Countly.m
*	modified:   CountlyDB.h
*	modified:   CountlyDB.m