Allow to drag and drop files, folders, documents and objects to the Property Editor in Workflow Designer

There should be a possibility to drag and drop next items to the Property Editor:

1. files
2. folders
3. folders from the projects
4. documents from the project
5. objects from the project

Widgets on the Property Editor that should process dropped items:

1. dataset widgets
2. URL line edits - if line edit allow several URLs, then a new one should be added to the end, else a new one should replace the old one.