Blender Git Loki

UI: Add 7 new community themes

This commit adds 7 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, Vojt?ch Lacina, Michail Soluyanov, Jason van Gumster, Mr Wax Police & Jonathan Lampel.

An overview is here: https://developer.blender.org/T74360