Improve wording for red eye reduction

Summary:
The command name shown next to Undo was missing some spaces.
On this occasion, let's change every occurrence to use the imperative mood,
which is what the other image operations are already doing.

Test Plan:
Edit → Reduce Red Eye, click on image, OK. Now look at
Edit → Undo, which should show the correct name.
Also check that no occurrence of the string was missed.

Reviewers: Gwenview, ngraham

Reviewed By: Gwenview, ngraham

Subscribers: muhlenpfordt

Differential Revision: https://phabricator.kde.org/D14407