String Freeze break for Tweaks

[Jeremy Bicha <jbicha ubuntu com>]

I would like to add a string for Tweaks 3.26.0. The string is for
allowing users to enable or disable the Activities Overview "hot
corner" (where the overview shows up when you push your mouse to the
top left corner without pressing any buttons).

The string is used in one place where it is commented out by default.
Ubuntu 17.10 (Beta) includes a patch from
https://bugzilla.gnome.org/688320 to enable turning the hot corner on
or off with gsettings. Ubuntu's "Ubuntu session" (a tweaked version of
GNOME) disables the hot corner by default. Therefore, the new Tweaks
string will be uncommented in an Ubuntu patch. Any other distros that
cherry-pick that patch are encouraged to enable that string too.

I intend to do a 3.26.1 release of Tweaks before Ubuntu 17.10's
release so that the new string is translated.

The string is "Activities Overview Hot Corner" and it's associated
with an on/off switch.
https://git.gnome.org/browse/gnome-tweak-tool/commit/?id=29073dd8a7

Thanks,
Jeremy Bicha