Implement CLI toolset for juicy elements

[tomalec]

Instead of gulp/grunt/bower bagic and repolepsy hell in merging -boilerplate stuff to each and every project, we could provide a set of scripts as npm package, similar to what Polymer does with polymer-cli. We could at least cover:

• init - that provides element boilerplate vanila or polymer one
• bump - that bumps the versions in all files, creates a tag and commit
• test - that executes CLI tests
• serve - runs polyserve
• watch - watch file changes

I would say that first two are crucial.

We can start with just forking polymer-cli.

WDYT @warpech?

[warpech]

This is now tracked in https://github.com/Starcounter/RebelsLounge/issues/25