Merge remote-tracking branch 'upstream/datajam' into datajam-any-xblock-in-studio

Conflicts:
	cms/envs/devstack.py
Use XBlock rather than XModuleDescriptor for access checks
Use XBlocks instead of XModules when loading
Allow use of any XBlock installed as an advanced component in Studio
Add a default studio view with instructions on how to edit an xxblock directly in mongo