Prepare Designer and Studio Elements for Polymer 3

The goal is to do some clean up on both studio elements and designer to prepare for polymer 3 migration.

Stuff to do in the scope of the ticket:

• improve the build process (remove browserify, babelify tasks)
• use a different approach for serving the app (in dev mode)
• clean up and normalize dependencies
• refactor the nuxeo-studio-elements (include a single bower.json file for packaging)
• update and clean up the catalog generator (maybe tackle the NXS-4754, it should come for free)