CMS: update of `cms-external-resources.xml`

* (addresses #493) (addresses #145) (closes #517) (PR #504)
fixtures: new name "CMS Learning Resources"

* (see PR #504)

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
testsuite: new file `cms-learning-resources.xml`

* (see PR #504)

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
templates: new name "CMS External Resources"

* Respects collection renaming in templates.  (see PR #504)

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