Use glib instead of libev

Use glib instead of libev

This commit ports awesome from libev to the glib main loop. This means that
awesome has fewer dependencies, because we were already depending on glib before
and now no longer need glib.

However, the main reason for this change is that, thanks to lgi, we have glib
bindings for lua. This means that lua code can add all kinds of event sources to
the main loop (timeouts, fd watchers, SIGCHLD watchers, ....). Yay

Signed-off-by: Uli Schlachter <psychon@znc.in>