This reverts commit 4524ba20.

ProtectedBranches model, Master permission for repo\n Allow push to protected branch for masters only

Project activities perfomance increased. Cache for project activitites disabled. Repository conception changed

This commit includes:

 * Projects can have zero or more WebHooks.
 * The PostReceive job will ask a project to execute any web hooks defined for that project.
 * WebHook has a URL, we post Github-compatible JSON to that URL.
 * Failure to execute a WebHook will be silently ignored.