Translation update (de-informal)

Translation update (ru)

Update French translation

Translation update (fr)

Translation update (uk)

Translation update (lv)

prevent hidden pages to be shown in trace

Support for configurable e-mail return path

This adds some simple defaults for the guaranteed placeholders. This
ensures plugins can safely use these placeholders even when a template
did not implement them.

Make security.png more descriptive

Translation update (sv)

Translation update (fr)

Translation update (de)

Access attempts to security.png are normally denied, so the name of the file will be more self-descriptive

Security: Prevent direct access to /vendor/ via .htaccess

Translation update (be)

comment out empty language string

Translation update (de)

The empty string is not translatable in the translation interface and
causes all languages to be <100%

This is an alternative approach to #2164

fix: prevent two selected options, b/c apparently 'String' == 0  

There was a bug, where the options array ['Auto', 0, 1] would result in
HTML option tags where both the 'Auto' and the 0 option were selected.

link the old version in MM when view it

This commit fixes a bug in the media manager when viewing an old version
of a media file. While, in case of an image, the old image would be
displayed in the third pane, the link above would still link to the
current version.

Fix section edit buttons for tables etc. 

Let `utf8_substr` use `utf8_strlen`