Allow using user ID in messages

hhucn/adhocracy.hhu_theme#431
add page options to model
create sectionpage template and css
hide subpages from index for sectionpages
recursively calculate latest activity time
check is_sectionpage recursively
create page comments view
hide pro/contral/neutral in comments form for norms
create amendment view
fix proposal create ret_url
apply Page.allow_selection option

I was not completely sure about the scope of this task.

If I have gone to far in some places it should be simple
to revert my changes
apply Page.allow_comment option

I was not completely sure about the scope of this task.

If I have gone too far in some places it should be simple
to revert my changes
Allow to render markdown text

I searched for a canonical way to render a text
but there seem to be dozens of ways to do that.
pep8
Fix socialshare text for page variants
Add optional query_string parameter to base_url function
Take query string into account in login_redirect_url
Fix comment wording for non-logged-in users
Use full width for section pages

This now hides the information box entirely. We have to find a new place
for it, e.g. hide it in an overlay...
Workaround: Increase overlay height to fit everything in

Dunno why $('body') inside the iframe doesn't return the correct height.