[#315] Change settings.DOMAIN_NAME to settings.RSR_DOMAIN

Change all uses of DOMAIN_NAME to RSR_DOMAIN
[#315] change settings.APP_DOMAIN_NAME to settings.AKVOAPP_DOMAIN

Change all uses of APP_DOMAIN_NAME to AKVOAPP_DOMAIN and use getattr()
where appropriate.
[#315] Change request.app_url to request.akvoapp_root_url

Change all uses of app_url to akvoapp_root_url in  views, templates and
template tags.
Move settings.DEFAULT_FROM_EMAIL from 90-finish.conf to 20-default.conf

Also fix the use of the setting in a couple of places
Change a number of references to www.akvo.org to akvo.org or
rsr.akvo.org as appropriate
[#315] Fix partner site widgets' links when running on CNAME

When a PS widget is shown using the CNAME domain for the PS the links
point to to the akvoapp.org domain.

Fix by using request.META.HTTP_HOST instead of request.akvoapp_root_url
(refactored from request.app_url) where needed or by just using the path
when constructing hrefs.
Update media assets
Merge branch 'feature/git_info' into develop
Merge branch 'feature/git_info' into develop
Merge branch 'feature/git_info' into develop
[#230]Fix fb:app_id tags
Merge branch 'feature/meta-tags' into develop
[#196]fallback image needs to be 200px square for fb to like it
Merge branch 'feature/meta-tags' into develop
[#196]Use Akvo logo if partner logo is too small for FB
Merge branch 'feature/meta-tags' into develop
Merge branch 'master' (v2.3.0) of github.com:akvo/akvo-rsr into develop
Merge branch 'develop' (with latest social media fixes) of github.com:akvo/akvo-rsr into release/candidate
[#316] Added fix to force rendering of a scrollbar in partner site project listing widget.
[#157] Renamed RightNowInAkvoResource.override_urls() method to prepend_urls() to prevent deprecation warnings in web server logs.