UI: fixes collection icon issue

* (closes #579)
* darkens a bit tags’ bkgd-color
LHCb: update of `lhcb-external-resources.xml`

* (addresses #145) (addresses #517) (PR #538)
fixtures: new name "LHCb Learning Resources"

* (see PR #538)
testsuite: new file `lhcb-learning-resources.xml`

* (see PR #538)
ALICE: update of `alice-external-resources.xml`

* (addresses #145) (addresses #517) (PR #552)
fixtures: new name "ALICE Learning Resources"

* (see PR #552)

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

* (see PR #552)

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
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>
ATLAS: new name "ATLAS Learning Resources"

* Introduces new collection and file name for ATLAS external (->
  learning) resources.  (addresses #517)

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
base: s/external/learning

* Respects recent renaming of "external" resources to "learning"
  resources.  (closes #517)

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
LHCb: update of `lhcb-tools.xml`

* Links to instruction page. (PR #584)
UI: makes homepage "action"-buttons more clickable
UI: updated breadcrumbs styling

* fixes alignment
* fixes “font-weight” to smh lighter
UI: updates macro for experiment "action"-box

* changes box-styling to be more unified across portal
UI: adds "action"-boxes to ALICE, LHCb

* adds “action”-boxes to education pages for ALICE, LHCb
* connects VM, GetStarted pages with education
* (addresses #573)
UI: changes intro text wording on the home page

* (closes #581)
overlay: cleaning code from alternative homepages