Parse less and scss files

This pull request is for [Simple support for LESS/SCSS](https://trello.com/c/KoK6kPtp/1190-m-simple-support-for-less-scss-in-key-brackets-features) with the exception of the following unchecked remaining development tasks.

- [ ] Don't show Quick Edit results for both generated CSS _and_ original SCSS/LESS file
- [x] Hook up nested selector support to Live Preview Highlight
- [ ] Unit tests: CSSUtils APIs with LESS/SCSS
- [ ] Unit tests: Quick Edit with LESS/SCSS
- [ ] Unit tests: Live Preview Highlight with LESS/SCSS ?


Of the 3 checks, `indexOf()` is most likely the slowest, so it should be checked last:

```JS
    return (state.state !== "top" && state.state !== "block" && stream.string.indexOf(";") !== -1);
```