Optimize terminal emulator rendering

[TheJJ]

Our terminal emulator is basically feature complete (it can run vim!), but the rendering is very slow and inefficient. Please optimize it.

The non-opengl-output can be tested with ./run test -d console::tests::interactive, you'll get a shell.

You should synchronize with #287 and in the chat room so that it is integrated with the renderer instead of doing the same things again.

libopenage/console/draw.cpp

Maybe you get some ideas here:

• https://github.com/kovidgoyal/kitty
• https://github.com/jwilm/alacritty