Fixes for previous / next buttons

A few bugfixes for the previous / next buttons when working with hidden QElements, or when dynamically inserting / deleting rows to the quickDialogTableView.

Also fixed a bug where QEntryElements would stay selected after pressing a previous or next button.

This branch also includes pullrequests #429 and #431 so it should be a simple fast-forward merge now.

I've closed those 2 pullrequests with a reference to this one.