Send-signal, payload if hook does not exit and cleanup.

* So, if "send-signal" is set in the hook.path field, a signal will be send with the repo, info, user and request. This allows to process the hook in an attached python method instead of a command /shell script that has to have the correct mode etc.

* The payload will be passed if hook does not exist.
But `info`, `repo` and `user` are all gathered before the `try:` statement.  The `try:` statement only tries to get the `hook`.