Add dbus interface to allow notification state manipulation from ui

notification_begin_req(string id, int32 length, int32 renew)

Starts notification exception state that lasts for length ms. Display
is turned on if proximity sensor is uncovered during that time. The
length is extended by renew ms while touch input is detected during
display on time.

notification_end_req(string id, int32 linger)

Ends notification exception state. The display is still kept on for
linger ms (or turned on if proximity sensor is uncovered during the
linger time). If touch input is detected during linger time, the
display state restore is canceled and normal blanking timers are
used instead.

Also add --begin-notification and --end-notification options to
mcetool to ease testing and debugging.

[mce] Add dbus interface to allow notification state manipulation from ui. Fixes JB#17383
Add D-Bus name owner monitoring for clients that hold notification slots

Start monitoring client when it succesfully adds first notification.

Stop monitoring client when it removes last notification.

Cancel all notifications from a client that drops from the system bus.
Merge pull request #152 from spiiroin/notification_dbus_api

Add dbus interface to allow notification state manipulation from ui
Remove unused display_state variable
Bump mce version to 1.29.0