WebLinkback: better URL title display

* Resolved XML entities in the title display
WebLinkback: better /linkbacks tab display

* Trackback URL displayed as link to simplify copy and paste

* Short trackback description displayed
WebLinkback: better global /linkbacks page

* Displays only records that are accessible by the user
WebLinkback: module optional

* Module can be disabled (closes #1245)
WebLinkback: better documentation
WebLinkback: minor improvement

* Renamed regression test method
WebLinkback: pending linkback notification emails

* Lists all pending linkbacks in one email (closes #1247)

* Enriched regression tests

* Enriched documentation
Merge branch 'pglauner/better-weblinkback'

* pglauner/master-better-weblinkback:
  WebLinkback: pending linkback notification emails
  WebLinkback: minor improvement
  WebLinkback: better documentation
  WebLinkback: module optional
  WebLinkback: better global /linkbacks page
  WebLinkback: better /linkbacks tab display
  WebLinkback: better URL title display

* Merge note: besides solving conflicts, amended webstyle_templates slightly.

Conflicts:
	config/invenio.conf
	modules/webhelp/web/admin/howto/howto-run.webdoc
	modules/weblinkback/lib/weblinkback_regression_tests.py

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