feat(app): Add jsPlumb dependency to app.

The Bower version of jsPlumb does not include a `main`
field in it's bower.json file.
The solution was to set an `overrides` field in
this project's bower.json field to patch jsPlumb's.

See
http://stackoverflow.com/questions/21357719/configure-grunt-bower-install-path-for-a-component/23436755#23436755