collections: fix "error" when coll. name is wrong

* redirects to “404” page when collection name given is doesn’t exist
* ( closes #452 )
UI: fixes bcg-color in "404" pages
CMS: external VM link -> opendata-link (recid-250)

* (closes #472)
UI: fixes dropdown menu overlapping

* ( closes #473)
UI: adds a homepage alternative as '/home8'

* ( addresses #467 )
UI: fixes/reverts logo to previous state