Summary:
disable the sorting for single album. does not make any sense, does not work. seems to have sneaked in during refactoring of the views
also override the sorting method for the album proxy model to be safe

Test Plan: no sorting button appears when viewing a single album

Reviewers: mgallien

Reviewed By: mgallien

Tags: #elisa

Differential Revision: https://phabricator.kde.org/D15486