Add session save.

The entire startup process has to be rearranged in order to make the
session restore work (it's a hell of a mess with dependencies between
different parts of the code).

Debug messages now use the correct format specifier for X windows.

Remove input bar (it hasn't been in stwm since... when?).

WARNING: The restarting process hasn't been tested on multiple monitors
yet.
Add workspace/resolution checks for Xinerama.

If a workspace gets swapped, they both get marked as dirty to force a
rearrange.

Furthermore, each workspace gets checked for emptiness upon hiding (to
make sure there are no unfocused empty workspaces upon removing a
monitor).
Merge branch 'restart'.

Add a savestate mechanism for saving the session. For further changes,
see the branch' changelogs.