Allow toggling debug verbosity with SIGUSR1 and SIGUSR2

Switch to debug verbosity with USR1 and back to warning level with USR2

[mce] Allow toggling debug verbosity with SIGUSR1 and SIGUSR2
Tune delays for display blank/unblank debugging led patterns
Do not blank screen if touch events are seen after alarm ends

Keep display on longer after alarm dialog is closed.

If touch events are seen during that period, do not restore the
pre-alarm display and tklock state.

[mce] Do not blank screen if touch events are seen after alarm ends
Add explanations for display blank/unblank debugging led patterns
Deal with dbus_connection_send_with_reply() returning NULL pending call

It is possible for dbus_connection_send_with_reply() to report no
failure, but still return NULL pending call object - for example if
the connection is in disconnected state - and thus we need to check
for this separately.
Merge pull request #113 from spiiroin/end_of_alarm

Improve end of alarm handling and other fixes
Bump mce version to 1.23.1