Adjusted the colors of the notifications and media controls to help them fit in better together.


This (partially) reverts commit 127bbdf653.
Only incorrect changes from Kirigami.Units.largeSpacing to
Kirigami.Units.gridUnit are reverted. Only Plasma.Units were buggy.
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.