Add needs_grading_count flag when fetching assignments

There's already a property for this on the model, but it
will never have a value because we don't fetch it.
add needsGradingCount to CKICourse

the property was there, but the mapping wasn't hooked
up so you were never getting any values
Merge remote-tracking branch 'instructure/CanvasKit/master'
refactor CKIAssignment
fixing up rubrics
add to umbrella header, clean up
make assignment groups return assignments
actually use params from last commit
minor adjustments to models

rename a few properties, adjust types, etc.
Merge remote-tracking branch 'instructure/CanvasKit/master'

Conflicts:
	CanvasKit.xcodeproj/project.pbxproj
fix project file:
Merge remote-tracking branch 'instructure/CanvasKit/master'
update podspec to v0.47
Merge pull request #122 from jarsen/master

Many things, but mostly rubric support