Allow for mac development

Some of the code was tied to UIKit, make it only included when doing
iOS development.
Actually allow for mac development

finally actually works.
Merge remote-tracking branch 'instructure/CanvasKit/master'

Conflicts:
	CanvasKit.podspec
	CanvasKit/Networking/CKIClient.m
get rid of some warnings
Merge pull request #81 from jarsen/master

Allow for Mac Dev