Merged feature/css and related-docs

@shahabl, I merged your branch with the latest related-docs as in sebaslv/brackets-livedev2#1 but created this new pull request to get busykai:develop as the integration point.

recursive scan of @imports wasn't included in the merge. I'll take that from your original branch and manually merge it on my new implementation.
 

This is basically continuation of, as I understand, how njx made this prototype.  Bringing in code from the current Live Development where modifications are needed.  We can rename this file, but I thought keeping the same name will make it easier to understand for someone comparing the original and this implementation.  I'll discuss with sebaslv.