in CountlyEventQueue remove event coalescing and simplify recordEvent methods; remove unneeded dealloc method; minor code formatting changes
use CACurrentMediaTime (requires linking to Quartz) instead of CFAbsoluteTimeGetCurrent in an effort to avoid negative session durations; in CountlyConnectionQueue, don't send negative session durations to the server
explicitly tell NSURLRequest to always ignore local cache data; if for some reason the NSURLConnection is not created, immediately end the background task