invenio2-kickstart: customization for zenodo

* Specifies the name of the CFG_INVENIO2_REPOSITORY_GENERAL directory

* Checks for bower-base.json existence
Overlays are installed using ``pip install -r requirements.txt --exists-action i``, and the overlay's requirement.txt already contains a line ``-e git+https://github.com/inveniosoftware/invenio@pu#egg=Invenio-dev`` (https://github.com/inveniosoftware/invenio-demosite/blob/pu/requirements.txt#L10) which will install Invenio (using the checkout).