invenio2-kickstart: customization for zenodo

* Specifies the name of the CFG_INVENIO2_REPOSITORY_GENERAL directory

* Checks for bower-base.json existence
This adds about ~1 min to the installation process, and ensures that assets can be build properly. If you run with ``ASSETS_DEBUG=True`` the build assets are just ignore thus you 'only' loose a bit of time.

I think instead of introducing too many CFG variables, it would perhaps be better if we could just use the .travis.yml file? Or the .travis.yml and kickstarter could use a common script.