abook: fix typo in variable name in search

The status_q variable was called q when including disabled
entried in the search (left-over from last search re-write).
templates/cams/participants.html: use url template tag

Instead of using hard-coded url tag from context, use
standard url template tag to find URL with its name
(groups in this case).
mgmt: convert groups views to CBV
abook: remove unnecessary order_by

The Contactable model now already has ordering property
set in its Meta sub-class.
mgmt: convert group view to CBV (GroupView)
pindown_group.html: use url built-in template tag
groups: convert pin down views to CBV

* add GroupBaseView to set the page title and get the group
  object in `get' method instead of `get_context_data' via
  new method `GroupBaseView._get_group_and_title'
* add PinDownGroupView to pin down a group
groups: remove unnecessary *args from get_context_data
browser.html: show total number of entries

Show total number of entries (not pages) at the bottom
of the browser template, near the bottom paginator.
rename participants -> groups in remaining places