Light and Black UI Theme

[dlvdls18]

Motivation
It's not a problem for me but it might help somebody else using your app.

Description
Add a light and black UI theme and ability to change the editor theme to monokai, tommorow night etc..

The only theme is Dim and it's just dark gray. Add light theme (not so light) and black theme (literally black, not just gray).

[benhatsor]

Cool, maybe the theme picker could look like the Telegram theme picker:

[dlvdls18]

Ooh, that's cool.
Yeah, like that.