Fix AppCatalog to use 'marker' attribute for pagination

Glance-like interface provides us with 'has_more_data' flag and
'marker' pointing to the next page data set. That means that
AppCatalog should drop link to previous page of Applications as well
as current page number - they both are not supported by standard OS
api.

Also:
* do not pass category as a part of murano:index url, pass it as a
  part of query-string (as well as marker);
* refactor filling 'Latest Apps' section: inside get_context_data()
  remove invalid app_id-s from session (i.e. because those packages
  were deleted). This change is needed because we may no longer know
  all existing packages after a single request to AppCatalog
  IndexView.

Change-Id: Ia0f4adb5657de9fba67733705268eb80684c656c
Implements: blueprint normalize-dashboard-pagination
Closes-Bug: #1307990
Closes-Bug: #1325362