Build workspace services using Gulp

- Rename `scripts/modules/common/workspace.js` to `workspace.services.js` to make it consistent with other source files providing services.
- Add a gulp build task to generate the services file using loopback-sdk-angular.
- Remove `workspace.services.js` from version control, as it is auto-generated now.
- Remove style.css from version control, as it is auto-generated too.

/to @seanbrookes @anthonyettinger please review