Console improvements

* Unused console backgrounds no longer take up memory
* Input cursor can now move left and right
* Support for selections (Shift-arrow keys, CTRL-A, etc)
* Clipboard support (CTRL-C to copy, CTRL-V to paste, CTRL-X to cut)
* Fixed handling of simultaneous modifier key presses

https://dl.dropboxusercontent.com/u/3518218/21/console.gif

None of this affects chat yet, that's not part of the console. I'll look at it later.

See merge request !133