Draw a status bar at the top, start handling fonts.

The status bar doesn't yet claim an area on the screen for itself, and
it doesn't yet show anything useful (just a test string).

Given that with a simple XDrawString(), font ascents/descents are not
well handled, positioning a text is quite cumbersome, hence I'm starting
with some XFont stuff now.
Add workspace dimensions and font handling.

Workspace dimensions are now used to set the layout (this allows to keep
the statusbar area free from clients). The font is loaded according to
the config, and its information (ascent, descent, height) is used to
correctly position the text in the status bar.

The font and status bar setup is moved to separate functions, and all
setup functions are prefixed with "init" (including setup() -> init()).
Display workspace position in status bar.

It's meant to display the workspace's name, or the coordinates if the
name is empty - which is currently always the case, since we cannot
modify the name yet.

The Graphical struct is now called DC ("draw context"); it's conform
with dwm, somewhat equally correct, and shorter.
Merge branch 'statusbar'.

Displays a status bar at the top of the screen with the current
workspace's name (currently it only displays the position, because there
is no way to set the name). The tiled clients get nicely arranged around
it, so it should never get covered.