Improve wording for red eye reduction

Summary:
The command name shown next to {nav 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:
{nav Edit > Reduce Red Eye}, click on image, {nav OK}. Now look at
{nav 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