Add more default color themes

I think we should provide more default color themes.

There are several well accepted and MIT licensed themes out in the wild.

e.g.

• MIT Dracula, dark theme

https://github.com/dracula/kate

=> added now, see !58 (merged) & https://kate-editor.org/themes/

• MIT ayu dark, mirage and light

https://github.com/dempfi/ayu

Seems like a good junior job/... to provide .theme files for these.

(and hunt down some more)

Soon KTextEditor will take these all up per default and allow people to just use them in Kate/KWrite/KDevelop/Kile/... without extra effort.

A good idea would be some generated web site to demonstrate the themes one one example file. Like the light/dark refs for the highlighting auto tests this could be one auto-test, to ensure all themes are usable.