add counters to project overview

[MyPyDavid]

This PR contains one of the features mentioned in #355.

• Adding a counter which shows the total number of projects that exist on the site
• Perhaps adding an additional counter which shows the number of projects which are currently displayed (after filters have been applied)

• Counters (numbers) were added to the templates

  • rdmo/projects/templates/projects/projects.html

  • rdmo/projects/templates/projects/projects_pagination.html

  • rdmo/projects/templates/projects/site_projects.html

  • "Search" renamed to "Filter Projects

  • a counter is placed under filter input block in small text:

    • add counters to project overview #606 (comment)
    • the number_of_projects for the user was added to the get_context_data of the FilterView
    • a counter at the footer of the pagination, which shows the number of projects in the current page

• add new translations

• a bugfix for the pagination in combination with filter was added in the context data of rdmo/projects/views/project.py:

  • added function in rdmo/projects/utils.py

def set_context_querystring_with_filter_and_page(context: dict) -> dict:
   '''prepares the filter part of the querystring for the next and previous hyperlinks in the pagination'''
   if context["filter"].data:
       querystring = context["filter"].data.copy()
       if context["filter"].data.get('page'):
           del querystring['page']
       context['querystring'] = querystring.urlencode()
   return context

• added tests in rdmo/projects/tests/test_utils.py

• a bugfix for Bug in display of "My Projects", single project(s) disappears from list or shown double (front-end, view queryset) #578 was added in the rdmo/projects/views/project.py

# the 'updated' from a Project should always return a valid DateTime value
# when Greatest returns null, then with Coalesce the for 'updated' is taken as fall-back
queryset = queryset.annotate(last_changed=Coalesce(Greatest(last_changed_subquery, 'updated'), 'updated'))

[coveralls]

Coverage: 90.724% (+0.3%) from 90.469% when pulling 84f9c01 on feature/355-add-counters-to-project-overview into 813df5e on dev-1.10.0.