gruntless invenio

Removing grunt from invenio, one dependency at the time.

**todo**:
- [x] bower.json dependencies should be empty.
- [x] updated documentation
- [ ] translations -> #828
- [ ] inveniosoftware/invenio-demosite#28
- [ ] files that where not in bower.json but are still present in some templates:
   - [ ] [recline](http://okfnlabs.org/recline/)
   - [ ] [mediaelement](http://mediaelementjs.com/)
   - [ ] `ui.datepicker.min.js`
   - [ ] `backbone`, `underscore`, `parsley`, `handlebars`, ... bibauthorid/templates.py

Closes #1842 
Which purpose does it serve?