Make theme/color_scheme optional

[mitranim]

Self-explanatory. This allows the user to opt out of Terminus's themes, and should address #5 in a clean way.

Since I'm not familiar with the codebase, there are likely to be eyebrow-raising or hair-raising changes. I'm absolutely not insisting on this to be merged, but rather it's a suggestion. Maintainers might envision a better way to do it.

[randy3k]

Unfortunately, we need to customize the theme in order to support the color highlight. An arbitary user theme won't work.

[mitranim]

Took some digging to realize what you're talking about. By pure accident, none of the tools I ran in Terminus so far use colorized output, so I wasn't even thinking of it. But this also showcases a viable use case. For some users, maybe all their tools' output is colorless, or they don't particularly care and just want consistency in ST. I think it's a useful option to have, especially before the adaptive theme. (Wouldn't have made the patch otherwise.) But of course it's up to you whether this functionality should be in the core.

[mitranim]

Maybe it should be noted that terminal color output in general is optional and can often be disabled, though I'm not sure if there's a conventional interface all such programs are expected to obey. In normal terminal emulators this opt-out is not particularly important. Terminus is a different case because it's embedded inside Sublime which already has its own themes and color schemes, so the opt-out becomes somewhat more important.