Fixed some hooks after recent GMod dev update.

Following garrynewman/garrysmod#579, hook.Call no longer assumes a nil hook table is a GAMEMODE table. This means that the gamemode function will not call if you do not pass GAMEMODE into hook.Call (or you use hook.Run or gamemode.Call instead).

* MySQL was broken because of this. GM:DatabaseInitialized was not called which meant DarkRP.initDatabase was not called. Fixed in this PR.
* OnPlayerChat and ChatText hook calls now call the GM function again. They are GMod hooks rather than DarkRP hooks so they probably should call the GM function.

Everything else _seemed_ to work.