replace <div class="hr"><hr /></div> by <hr />
adopt stylesheets to use hr instead of .hr
replace <hr /> by css border in content_list elements
pep8
refactor flash_message
refactor info_box
refactor overlay
use our info_box instead of bootstrap alert
rm bootstrap_alert
rm simple_overlay
[scss] some css gradients
fix sidebar_nav background offset
[scss] themable sidebar_nav
fix fallback background colors in sidebar_nav
[scss] themable facets arrow
Add serve http error view

This adds a view to the error controller which serves an HTTP error
page, which can be defined by setting
`?force_status=503&hide_code&hide_notify` or similar.

This can be used for example to create static maintanance pages served
by a frontend webserver.
Simplify conditional (trivial)
Fix poll caching (fixes hhucn/adhocracy.hhu_theme#391)

Add session id to the cache key of poll and comment tiles.

This remedies CSRF alerts and thus broken poll widget, if a user
revisits cached tiles with a different session, e.g. by using a
different browser or logging out and in again.
Merge pull request #467 from nidico/feature-fix-poll-caching

Fix poll caching (fixes hhucn/adhocracy.hhu_theme#391)
Use CSRF token instead of session id as cache key.

Cookie-based sessions don't have an ID.