global: use of demo.invenio-software.org

* Uses `demo.invenio-software.org` instead of `invenio-demo.cern.ch'
  everywhere.

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
docs: author sorting including first names

* Sorts authors alphabetically according to first names, as sorting by
  family name and printing by first name did not look consistent.

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
docs: removal of explicit Contributors section

* Removes explicit Contributors subsection that was the only one making
  Table of Contents non-flat.

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
docs: better description of Invenio-Client

* Changes description of the Invenio-Client package in various places
  for better wording describing the client.

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
global: s/Invenio Client/Invenio-Client/g

* Changes visible name from "Invenio Client" to "Invenio-Client" in
  order to be consistent with the (lowercase) package name.

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