[evolution] gnome-3-22 String freeze break plea

[Milan Crha <mcrha redhat com>]

        Hello,
I'd like to commit a change for bug:
https://bugzilla.gnome.org/show_bug.cgi?id=776391
also into the gnome-322, but as the Evolution localized also GSettings
keys, then it breaks the string freeze policy. As mentioned, the new
translatable strings are only for the GSettings keys, thus shown only
in the dconf-editor or such tool, where users may not usually want to
go, thus I think it's pretty safe to make the change. The added option
is supposed to be hidden, it's not anywhere in the UI and is only for
the developers, but influences how the Evolution behaves for regular
users, in a not so great way. That's the main reason why I'd like to
commit also to the stable branch.

The added strings are:
 <_summary>Enable special WebKit developer features</_summary>
 <_description>The change of this option requires restart of the Evolution.</_description>

I plan to make the final 3.22.5 Evolution release on February 13th.
        Thanks and bye,
        Milan