Draft: window: Add corner tiling

This allows users to put a window in each corner of the display.

Fixes: #2128

Current problems with this patch:

• No keyboard shortcuts to tile into each corner. I believe having shortcuts like Super Left and then Super Up to move a window to the top left corner would make sense, but Super Up fullscreens windows
• Cannot resize windows in a corner up or down
• When opening a window, putting it in a corner, and then opening another window, a blue box appears

I'm not sure what the best way to fix these problems would be.