TerminalWidget was relying on the "window became active/inactive"
events from WindowServer to update its own internal focus state.
Unfortunately those events are only sent to the window's main widget,
so this was not working when the TerminalWidget was embedded deeper in
a widget tree.
This patch hooks the focusin and focusout events and uses those to
set the focus state when received. This makes TerminalWidget behave
nicely in both configurations. This design is kind of a workaround for
this awkward focus architecture and we should figure out something
better in the long term.
