Show all news about a Community, view function + template + unittests

changed show_all_news to show_community_news

Flake8 errors

Added template
Merge branch 'Show_all_news_of_a_community' into demo

Conflicts:
	systers_portal/dashboard/models.py
	systers_portal/dashboard/tests.py
	systers_portal/dashboard/views.py
	systers_portal/systers_portal/urls.py