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
Network test for fetching all quizzes for a course
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
Merge pull request #4 from mileswright/master

CKQuiz API Enhancements
Improved login error handling. Removed the domain from the prepare methods for canvas kit. Added the domain as a param for user login
Merge pull request #5 from elgreco84/master

Improved login error handling. Removed the domain from the prepare metho...
Added Model w/Tests for External Tools API
Added Networking w/Tests for External Tools API
Merge remote-tracking branch 'instructure/CanvasKit/master'

Conflicts:
	CanvasKit.xcodeproj/project.pbxproj