V2.0 jazzcat improvements

Alright this is a big one. Changes:

- Have the option to use Jazzcat without concatenation
- Use Jazzcat with a JS response type as well as JSON
- `combineScripts` -> `optimizeScripts`
- No longer insert loaders with regular expressions.

Also, this was branched off of this: https://github.com/mobify/mobifyjs/pull/180. Merge it to have a less cluttered comparison!