Confusing live preview workflow when used with files outside of the current project

[jasonsanjose]

1. Open any project
2. File > Open... and choose an HTML file that is not in the current project's tree
3. Start Live Preview
4. Observe file: URL
5. Try live HTML editing - Fail
6. Open or drag in a CSS file that's associated with the HTML file
7. Try CSS selector highlighting and Live CSS editing - Pass

A user might incorrectly expect live HTML editing to work in this case.

It might be better if we nag the user somehow (maybe a status bar message or some other notification) whenever certain live preview features are disabled.

[redmunds]

What about adding text to the initial Live Preview modal informational (i.e. "we'll only show you this once") dialog that says something like:

"Live HTML (and any other features?) only work for files in current Brackets project and when using the Brackets built in server."

Note 1: We never really explain what a "Brackets project" is
Note 2: The "Brackets built in server" probably needs more explanation