Move GM hooks to where they belong

* Removed GM:PlayerDealth from cl_init since it's never called there
* Moved GM:OnPlayerChat to cl_init since it's a clientside only hook
* Made GM:GravGunPickupAllowed shared
* Moved GM:CanPlayerUnfreeze to to sandbox/player.lua since it's
serverside only function
* Moved GM:PlayerAuthor to serverside
* Removed GM:CanPose, GM:CanRender, GM:CanConstruct and GM:CanConstrain
since they are never called at all
* Removed GM:GetVehicles because there is no reason for it to exist, it
is never called and it serves no purpose
* Made so that the vehicle camera doesn't collide with anything but
world, this is to prevent third person fucking up when you have attached
props to the seat
Merge pull request #589 from robotboy655/realm

Move GM hooks to where they belong