We so far have been recreating the background elements for all the item throughout the shell. This merge request simplifies this by unifying these elements into a single component, making is easier to keep things at a consistent design while also being able to adjust things when needed in the future.
Per request, I tried to keep thing looking mostly the same as before.
The first picture is what the action drawer looks like now, the one after is with these changes.
Adjusted the colors of the notifications and media controls to help them fit in better together.
Move from a C++ library + QML plugin to a QML plugin only for simplicity, since the homescreen switching architecture will be done from Plasma, and so use of the shell library only needs to be from QML.
