Add Colorscheme Options

[MoonPadUSer]

This PR adds the option to choose between 2 colorschemes, one of them being the default red eclipse colorscheme and the other being an experimental blue nebula colorscheme I created, this is mainly to provide an easy way for users to try out colorschemes and give feedback

[voidanix]

1. This does not work apparently, seems to fail with a unknown command: setcolors in the console when pushing the 2 new buttons.
2. The active button and the pick a colour for the variable /ui_color_active seem clunky and confusing.
3. Got some whitespace at https://github.com/blue-nebula/base/pull/214/files#diff-59c8b041b4a3f9cd0dfa9d5311b1a7994a540dff82848bb05970571c99ee7f7eR306
4. The colorscheme_ "containers" (?) should probably have a docstring e.g. why is the default one resetting vars?

Barely knowing any cubescript at all, this is only a general review but hopefully you get the idea.