Made it possible to copy and build from source
Solved a few issues:
- XCode 6 stopped creating projects with Prefix.pch files making it impossible to manually build the Mixpanel folder in a new project. We removed our own pch file and imported UIKit as required.
- Removed calls to MPLog. They were causing spam in production apps, and we should only be using MixpanelDebug and its counterparts.