Allow windows to opened in reverse

[uri]

It would be nice if there was an option to reverse the tree. For example when opening a new window it would appear on the left instead of right. Or if the screen is more tall than it is narrow to open the new window above instead of bellow.

[koekeishiya]

Implemented on master.

New config window_placement, e.g:

# spawns to the left if vertical split, or top if horizontal split
yabai -m config window_placement first_child

# spawns to the right if vertical split, or bottom if horizontal split
yabai -m config window_placement second_child

[uri]

Works great!