xannounce: refactor font selection logic

Create a routine for font selection to clean up the main routine.

Signed-off-by: Trevor Woerner <twoerner@gmail.com>
xannounce: refactor font selection

Choose font from an array of names (makes it easier to add/remove names as/if
necessary).

Signed-off-by: Trevor Woerner <twoerner@gmail.com>