Display current project name in main window

Supersedes #6878.

This implements #2281, displaying the project name in the Brackets window title.
@le717 We decided originally we want to match each platform's standard separator, so can you please keep the split?  `\u2014` looks weird on Windows (doesn't match any other app), and `-` looks weird on Mac (same reason).  We want to feel as much like native code editors as possible.