Use the GUI module directly

The GUI module most probably did not exist yet when this code has been written. :)
Log going in and out of fullscreen
Add support for manipulating fullscreen state by messages

Note that the Python-side fullscreen interface is not supported by the Qt 5 GUI
module, the GTK module supports it just fine. Not sure about the Qt 4 GUI.
Use the GUI module for checking and manipulating fullscreen state
Remove fullscreen handling functionality that has been moved to the GUI module

The display module predates the GUI module, but GUI module now handles fullscreen
state changes, so remove the old fullscreen handling code from here.
Remove the old update() function an related machinery

Rana & modRana used to have a 100 ms (!) timer polling all (!) modules,
with the modules checking the clock to see if it is time to do something
or if a given poll call can be skipped. As you might imagine it was
horrendously inefficient (double so on a battery-powered device) and
thankfully has been replaced per-task timers long time ago.

Still, there were some remaining non-functional pieces (actually the
100 ms timer has still been enabled but errored out due to wrong
function signature) and there were now removed.
Make it possible to tweak the Sqlite tile database commit interval
Log how many tiles have been committed in the given Sqlite tile database commit