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 pull request #83 from derrh/master

Properly implements NSCopying. Adds fetchCurrentUser
Merge pull request #84 from derrh/master

v0.42
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
add submission fetching
add CKISubmissionSet
add networking for CKISubmisionSet
add userID to CKISubmissionSet
make userID property on CKISubmissionSet actually work

use the provided setter, duh.
update podspec to 0.44
Merge pull request #85 from jarsen/master

Submissions
add attachments to submissions
add CKISubmissionSet to umbrella header
Add CKIMediaComment

and group all the comment stuff together in the project
add mediaComment to submission object
Add cookie for future update to canvas login
Merge pull request #86 from jarsen/master

Submission attachments and media comments