Wavelet decompose logical fix

Patch by: Miroslav Talasek

Summary:
at first: wavelet decompose is in menu image so as source pixels cant be layer but visible image
at the second: new layer group must be added at top not with index 1 (i apologize ;))

Reviewers: rempt, dkazakov
Reviewed By: dkazakov
Differential Revision: https://phabricator.kde.org/D2429