improvement for SD-491: text items creator

Added the list of creators to the text items. One can see now the original creator of the item and the list of all creators who ever made changes to the item. Also the number of the modified version is available with the corresponding creator.
it shouldn't be a list. there could be `creator` which never changes and `version_creator` that does change. and given that we store all the versions we can get all the authors, but if you just fetch latest version you should get who created it and who created the story, not who created all the versions of the item..