[notifications] Add x-nemo-display-on hint

When this hint is set for a notification, the display will be turned on
when feedback is played.
[notifications] Allow clients to override category hints

Hints specified by clients will override those defined by the category,
to allow clients to selectively customize their notifications.
Merge pull request #95 from xknight/master

[lipstick] Synchronize application clipboard with the compositor
[lipstick] Move notifications db to centralised storage location

Previously, the notifications db was stored under
~/.config/lipstick/notifications.db

This commit changes the location to being:
~/.local/share/system/privileged/Notifications/notifications.db
Merge pull request #102 from special/notification-categories

[notifications] Allow clients to override category hints
Merge pull request #97 from special/master

[notifications] Add x-nemo-display-on hint
[lipstick] Reconnect to PulseAudio D-Bus API if initial connect fails.
Merge pull request #103 from chriadam/master

[lipstick] Move notifications db to centralised storage location
[lipstick] Get initial value of safe volume.
Merge pull request #104 from jusa/dev

Reconnect to PulseAudio D-Bus API if initial connect fails.
Merge pull request #106 from SamuelNevala/11382

[lipstick] Get initial value of safe volume.
[lipstick] Fix build.
[lipstick] Connect notify signal for window title changed

When the surface's title property changes, send a notification. Also
establish a slot for handling for future surface connections.