use the glib main event loop

use the glib main event loop

This big patch replaces our custom main loop with the event based glib
main loop.  This has several advantages: we can make all the tiny code
bits in the main loop independent from each others, we can add
additional file descriptors for polling (e.g. the mpdclient socket).

We don't need the ncurses timeout() anymore, because glib will poll
stdin for us.