Display current project name in main window

Supersedes #6878.

This implements #2281, displaying the project name in the Brackets window title.
Actually, after the split-view refactoring, it looks like this can never get called anymore with `ProjectManager.getProjectRoot()` uninitialized... so we may not need a no-project-open case at all.  Though it might not hurt to keep it just for robustness / future-proofing.  Up to you.