invenio-setup-prerequisites: skip extra reqs

* Skips silently when cannot install extra requirements
  such as ipython that are really not necessary.

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
invenio2-kickstart: initial release

* Initial release of the Invenio 2 kickstarter, permitting to bootstrap
  Invenio 2 based development environments on fresh OS in an unassisted,
  fully automated manner.  Tested on Ubuntu/trusty64.

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>