UI: Add 6 new community themes

UI: Add 6 new community themes

This commit adds 6 themes submitted by the community on Devtalk.
These themes both serve specific purposes, provide a greater variety in
look & feel, and serve as welcoming homes for users coming on board from
other packages. This is the initial commit, but these themes can be
continuously updated over time to fix issues and keep them up to date
with changes.

Thanks to all contributors, and in particular the makes of the picked
themes: Pierre Schiller, Edward Agwi, Vojtěch Lacina, Michail Soluyanov,
Jason van Gumster, Mr Wax Police & Jonathan Lampel.

An overview is here: T74360