Add tile keybinds (Fix #104, #127)

Hello:

The requested feature in Issue #104 and #127 was for a key-bind to tile the windows not just move them to the side. The commit messages are fairly documented but to summarize.

The 1st commit adds the schema data.

The 2nd commit refracts code from the unused function "handle_toggle_tiled" and puts it to use in handle_tile_to_side_backend. The refracted code is untouched.

The 3rd commit fixes 3 bugs which makes the new key-bind play nice with existing key-binds. These bugs for the most part are old existing bugs which I found while testing that the pull request works.

I tested this with on a completely up to date Debian/sid system.

Note: I forgot  that using '#' in the commit messages make github reference that pull request number. Sorry about that.

Hope this helps.