Added sh_cheats

For toggling cheats mode.
Slight AFK tweak
Significantly improved SGUI

SGUI now has a window manager, and events are called in the proper
order. Higher up windows get events called before lower ones, and
visible focus changes take place when you click on a lower focused
window.
Fixed panel auto sizing

It was incorrect before. Also now it doesn't create vector objects every
time it works it out.
Small chatbox fix

When going over the message memory limit, a fairly large space would be
created at the top of the message list.
ToString fails too much
Better mouse control

So objects don't shut off the mouse cursor for each other.
Cleanup stuff

Removed all the scattered is<type> functions and replace them with one
global function.
Added plugin network message framework.

Makes network messages way easier for plugins, and ties the receiving
into the plugin objects directly.
Added option to ignore spectators for afk kicking
Merge pull request #208 from Person8880/develop

Major SGUI changes, and plugin network messages