Fix age display: use a blocktrans instead of {% trans 'ago' %}

In some languages, like french "ago" is a preposition, so doing
something like "{{ value }} {% trans 'ago' %}" will not work, we have to
use a blocktrans.
Properly escape comments in comment_filter template tag.
Bump grappelli/filebrowser versions.
Version bump to 1.4.6
Added tag 1.4.6 for changeset 94f1427035e1
Update auto generated CHANGELOG, requirements, settings docs.
mezzanine.accounts czech translation update