fixtures: addition of LHCb collections

* Adds three LHCb collections ("LHCb Derived Datasets", "LHCb Tools",
  "LHCb External Resources") together with simple portalboxes.
  (closes #321)

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
fixtures: addition of ALICE External Resources

* Adds new collection "ALICE External Resources".  (closes #476)

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
ALICE: update of `alice-reconstructed-data.xml`

* Updates `alice-reconstructed-data.xml` with event number
  information.  (PR #483) (see PR #463)
fixtures: collection "CMS Open Data Instructions"

* Adds new collection "CMS Open Data Instructions".
  (addresses #441)

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
ATLAS: new file `atlas-derived-datasets.xml`

* Creates `atlas-derived-datasets.xml`.  (closes #438) (PR #455)
docs: new file `atlas-derived-datasets.xml`

* Updates installation instructions after addition of new file
  `atlas-derived-datasets.xml`.  (see PR #455)
LHCb: new file `lhcb-external-resources.xml`

* Creates `lhcb-external-resources.xml`.  (PR #465)
docs: new file `lhcb-external-resources.xml`

* Updates installation instructions after addition of new file
  `lhcb-external-resources.xml`.  (see PR #465)

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
docs: add new data files for installation

* Adds new data files to installation instructions.

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