UI: fixes in backward navigation

* backsard navigation now works in Educate, VM, Getting-started pages
(closes #243)
CMS: new collection of External Resources

* Adds new collection of "CMS External Resources".  (closes #253)

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
templates: removal of UserEcho

* Removes User Echo.  (addresses #258)

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
templates: about this portal

* Adds text for About this portal.  (addresses #65)

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
templates: collection page UI amendments

* Renames `Collection Items` into collection-specific phrase.

* Moves portal box to be displayed after collection name.

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
templates: safer display of imprint

* Safer display of imprint that may be missing in some collections.
  Fixes traceback when displaying "CMS External Resources".

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
views: code kwalitee improvements

* Improves code kwalitee of `views.py`: changes indentation from tabs to
  white space and amends PEP8 kwalitee.

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
collections: new regular/virtual collection setup

* New collection setup in which experiments are attached as virtual
  collections under Home and dataset/tools/etc collections are attached
  both under their experiments and under Home as direct daughter
  collections.  This eliminates extra level in the collection hierarchy,
  making facets work better.
  (addresses #70) (addresses #175) (addresses #258)

* Amends "For Education" and "Collection overview" pages accordingly.

* NOTE When other experiments join in, we may need to revisit this,
  e.g. introduce separate facets for separate experiments.

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
templates: no "lorem ipsum" in collection overview

* Removes "Lorem Ipsum" that was still left on the collection overview
  page.

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
templates: no preview for CMS Collections

* no preview for CMS Primary Datasets, CMS Validated Runs (closes #273)
collections: passing records on collection

* updated collection overview, with record samples passed as arguments
* new layout for “ CMS External Resources” collection page
records: page for "CMS External Resources" records
UI: homepage + entrypages(edu/rsch)

* new “svg” logo
* new home+education+research pages (Laura’s latest design)
* (addresses #218)
templates: fix link to latest CMS VM image

* Updates links to new CMS VM image in web page template and in the
  record itself.  (closes #185) (PR #276)
UI: "Introduction"->"Experiments"

* "Introduction"->"Experiments" (close #279)
* Removes validated run in the CMS education page (close #278)
homepage: adds testimonials

* (addresses #19 #231)
docs: more details about git workflow

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
docs: more details about after-merge updates

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

* corrects file path for json
news: removes links on authors