Add bowerrc

* https://github.com/yeoman/generator-gulp-webapp/commit/c6b693a01f2ef03ebba6c440db55cbf6b70892e7#commitcomment-7201413
* yeoman/generator-webapp#403
* yeoman/generator-webapp#393
* yeoman/generator-webapp#367
* yeoman/generator-webapp#398
* yeoman/generator-webapp#346
* https://github.com/yeoman/generator-webapp/pull/340#issuecomment-41430042
* ...

I'm aware that most of these are related to generator-webapp, but I don't see why these issues wouldn't be relevant here as well.

I would like to add it back in the generator-webapp as well, if this gets pulled.