installation: cleanup requirements

* Removes all packages except from invenio, Flask-Admin and workflow.

* Updates Flask-Admin to 1.0.9.dev0 version.

Signed-off-by: Harris Tzovanakis <me@drjova.ch>
Reviewed-by: Jiri Kuncar <jiri.kuncar@cern.ch>
travis: addition of required --yes-i-know argument

* Amends usage of `inveniomanage demosite populate --yes-i-know`
  command.  (addresses inveniosoftware/invenio#2294)

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
setup: fix link to __version__ treatment guide

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