Display current project name in main window

Supersedes #6878.

This implements #2281, displaying the project name in the Brackets window title.
I'd do OS differentiation like this:
```js
var osDash = brackets.platform === "mac" ? "\u2014" : "-";
var WINDOW_TITLE_STRING_NO_DOC = "{0} " + osDash + " {1}";
var WINDOW_TITLE_STRING_DOC = "{0} ({1}) " + osDash + " {2}";
```