This commit lets the 'move' command apply to floating containers as well
as tiled ones. The command may be appended with a number of pixels and
then optionally the string `px` (like '10 px') in order to move the
container more or fewer than the standard ten pixels.
Add swayc_change_layout function, which changes either layout or
workspace_layout, depending on the container type. Workspace being
always L_HORIZ makes this much more i3-compatible.
