Fix bower windows

This pull is designed to make a Windows user's life easier by trying a little harder to find `bower` in the new `addNewWidget` set of functions.  In Windows, it is conceivable that `bower` will be installed as needed without the `PATH` environment variable including its location.  I added a new `find_bower()` function that also looks in the default `npm` modules directory in `Sys.getenv('APPDATA')`.  While this is not perfect, it might ease the life of a poor Windows user like me who constantly faces `PATH` issues.

Non-windows users, **please test** to make sure I did not break functionality for the more sophisticated and wise Apple and Linux users.