New UI: Plasma desktop

Well... "New". Basically one extra package to our already existing KDE/Plasma base.

It boots into Wayland mode (I don't really care for X11 on postmarketOS), but if an user installs just plasma-desktop and not postmarketos-ui-plasma-desktop, they can always run it in X11 instead if they'd like too.

Booting in Qemu is a bit slow so after the loading circle disappears on the splash screen, give it a few seconds and it will show the desktop.

From my testing there are 3 issues so far:

1. The startplasmacompositor script that's used for launching the desktop, does calls to qdbus. However, that binary is called qdbus-qt5 in the upstream packaging. Either the user has to manually replace the calls in this script or we will have to find a solution with upstream to resolve this
2. Fonts in konsole (and possibly other applications) are messed up (see screenshot). Note that I added no spaces after that sentence. It seems there is an incorrect amount of space between each character, even making commands unreadable if short like ls, because they appear inside the prompt.
3. systemsettings doesn't launch.

qemu-amd64:~$ systemsettings5 -platform wayland
QCoreApplication::arguments: Please instantiate the QApplication object first
"Session bus not found\nTo circumvent this problem try the following command (with Linux and bash)\nexport $(dbus-launch)"

Installing dbus-x11 and then running export $(dbus-launch) does indeed fix this, but I prefer not doing this every boot. I'm not entirely sure how to fix this.