Some improvements/fixes for KPhotoAlbum

Apart from the positionable tag implementation (on which a pull request is already going on), I propose to include some other (smaller) bugfixes and new features into KPA.

This fixes Bug #256251 as well as Bug #269687 and adds additional functionality I personally have been always missing. I think these changes are quite handy – I hope you also do ;-)

I would love to see this to be included in the next release!