Add basic CKUser networking

And tests for CKUser.
Move user searching method

Moved the method for searching for users in a course to
its appropriate home.
Move user search functionality to user
Merge pull request #1 from jarsen/master

CKUser API Enhancement
Merge remote-tracking branch 'instructure/CanvasKit/master'

Conflicts:
	CanvasKit.xcodeproj/project.pbxproj
	Pods/Pods.xcodeproj/project.pbxproj