Fix Chameleon 2.14 compatibility.
Add fallback button in addbar

This fixes a bug introduced in 1e21ae1e6de6b49fb53ca462f1ddcc8d2aa6ce25
which made all add-buttons for non-survey content disappear.
Prepare 6.2 release.

Conflicts:
	docs/changes.rst
	setup.py
Onwards

Conflicts:
	setup.py
In the client, write the current language as class into the body tag, so that
language specific CSS rules can be applied.
Add a test that demonstrates the error reported in #99