This allows the title's texture to always be the full width of the text,
and clipped at render time according to the desired width (eg. tabs...).
As an added bonus, the texture no longer needs to be updated when
containers are arranged.
Implements rendering of borders. Title text is still to do.
Implements the following configuration directives:
* client.focused
* client.focused_inactive
* client.unfocused
* client.urgent
* border
* default_border
Replaces arrange_windows() with arrange_root(), arrange_output(),
arrange_workspace() and arrange_children_of().
Also makes fullscreen views save and restore their dimensions, which
allows it to preserve any custom resize and is also a requirement for
floating views once they are implemented.
