BackgroundCache: plug an Animation object leak

We need to return early in case the animation file is the same,
otherwise we'll create a new Animation object and leak the previous
one.

https://bugzilla.gnome.org/show_bug.cgi?id=739252
messageTray: Summarize notifications when messages queue up

It is really annoying for the user to acknowledge multiple notifications
when they queue up. So, to prevent a notification flood that has to be
handled by the user one-by-one, a summarized-notification feature is
added which leaves a single summarized-notification for the user,
replacing multiple notifications if the number exceeds 1, which they may
or may not acknowledge. When this summarized-notification is acknowledged,
the message-tray is opened where they can view the notifications that were
summarized. This helps the user concentrate on his primary task
simultaneously informing them about the new notifications.

https://bugzilla.gnome.org/show_bug.cgi?id=702460
theme: rewrite to be structured

- using SASS
- trying to reuse as much of the gtk adwaita as possible
theme: use Adwaita dark style for popup menus

- cannot sue box-shadow sadly.
theme: update some svg assets to adwaita 3.14 counterparts

- switches
- checkboxes
theme: fine tune scrollbars
theme: modal dialogs and tweaked entries
theme: top bar styling.
theme: overview search bar styling
theme: checkboxes
theme: top bar appmenu etc.
theme: volume/mic slider
theme: switches
theme: forgot old overrides of the panel styling
theme: top bar active is underlined.

- glow feels foreign, will be phased out
theme: remove unused assets
theme: overview styling

- still some quirks
- boy is this unstructured mess a pain to clean up :(
theme: workspace pager in overview
theme: entry selections, parsed css
appDisplay: Show a dot when application is running

Show a dot in running applications.
Design request.