create amendment view
fix ret_url for proposal create
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 minimum height to sectionpage body
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...
Allow non-formatted section pages
Workaround: Increase overlay height to fit everything in

Dunno why $('body') inside the iframe doesn't return the correct height.
pep8: Use proper check for empty string
Allow to disable propsal-norm selections despite activated norms

This can be useful if norms are used in context of section pages, but
shall not be connected to "real" proposals.
Do not show sectionpage change proposals in proposal list
rename show_in_list to is_amendment
Take comment.wording setting into account in sectionpage
hide show_proposal button in amendment view