Add dynamic overlay for email validation everywhere

Addendum to 796642897c1bf08f96ca9a7dbec000ea5b993f29
Fix validate email overlay

bd080977d6b9998b1744c96b9e1842d8e0fd8d92 erroneously used button and
text from join...
Add another jquery quirk to fix dynamic overlay

In some cases, getTrigger() returns a jquery object, which returns a
title when using `.data('title')` (e.g. add comment), while in other
cases, `.attr('title')` must be used (e.g. propose new norm).

As I don't find the reason for this (this might perfectly be a bug in
jquery / jquery-tools), we just check for both.
Fix redirect when logging in / registering on-the-fly (fixes #158)

Previously, the came_from parameter wasn't used.
Correctly add came_from to query string

Previously, existing query string parameters have simply been stripped.
Add force_path parameter to ret_status and friends

This parameter allows to force a path directly, even if entity is also
set.
Allow came_from parameter in Instance.join and User.resend

and make use of it from the corresponding dynamic overlays.
i18n: extract new messages
i18n: Update German translation
i18n: Updated other translations
Merge branch 'develop' into milestone_easier_buildout_merge_develop