We don't execute web hooks when:
 * You create a new branch. Make sure you first create the branch, and then push any commits. This is the way Github works, so its expected behavior.
 * When tags are pushed.

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.