improved error handling for short and broken videos
Enable positional tags in the database.

Original patchset by Tobias Leupold; I reworked the changes to
ImageInfo::rotate().
Added a "positionable" property to the Category settings dialog.

Original patch by Tobias Leupold.
GUI-Changes for implementing positionable tags.

Original patchset by Tobias Leupold.
This patchset also reimplements handling of image rotation in the
AnnotationDialog, fixing bug #336094.

CCBUG: 336094
CCBUG: 292900
Use database version 4 if positionable tags are used.

The version 4 database format is backwards-compatible to version 3,
but when saving the database in the older KPA version all positionable
tags will be lost.

As long as positionable tags are not used, new versions of KPA still
save the database in the version 3 format.
Make some i18n messages more readable/translatable.
Fixed area mapping when the actual image size is not known yet.
Fixed rotation again. Additionally, the fetched image size is now stored if the database is stored.
Minor style adoption for Viewer/TaggedArea.
Add Tobias Leupold to authors.