A bit of work for positionable tags

Hi there!

Some time ago, I requested a new feature for KPA on bugs.kde.org: tags with coordinates (cf. https://bugs.kde.org/show_bug.cgi?id=292900 ). I just tried to do a little bit of the work necessary to do this. I added an "positionable" property to the categories by adding a respective checkbox to the settings UI and integrating this property in the XML data structure.

I'm afraid the rest is beyond my C++/Qt coding skills – this is my first doing something with C++/Qt. Anyways, I hope I could help a bit and somebody may be interested in this.