Set Parse-RACExtensions submodule
Fix issue in activity view.

Cherry-picked from ParsePlatform/AnyWall@0acd62f36bf3de37caa0718edd91ab9cb25ee961
Explain fork in README
Prepare PAWNewUserViewController for RAC conversion
Use a signal to enable/disable the done button
RACify user sign up sequence
Add validation & error checking
Use command to power done button