Make Client.*Manager initialization lazy to reduce footprint.
Clean up method.
Add target domain to CanvasConfig

Canvas authorization requires that a particular auth token be used in
conjunction with a specific *.instructure.com/api/v1 instance.
Fill out the Account model.

Experimentally derived due to incomplete API documentation.
Change Account.*StorageQuota type to int.
Add AccountsManager.GetAll deserialization test.
Align test namespaces core library namespaces.