The editAssignment API now can take an Assignment.

The new overload takes an edited assignment then pull the data from the assignment to send to
the server.

The old method has been marked as Depercated.

Also added new members to the Assignment modle

the getGradingType(Context context) has been marked as Deperacated and been
replaced with getGradingType().

Added a getGradingTypeFromAPIString(String gradingType) method.
Added new setters to Assignment modle
Merge branch 'editAssignmentAPI-rf-update' of https://github.com/nbutton23/CanvasAPI into editAssignmentAPI-rf-update

Conflicts:
	src/main/java/com/instructure/canvasapi/api/AssignmentAPI.java