[CHG]GMO: first part of the new feature that makes the fact list editable.
The "value" field of the Properties windows has been made editable, but the fact list in itself is not yet updated whenever the value changes.
[FIX]GMO: to freeze the code, a dependency was missing because it was only loaded dynamically.
The dependency on SQLAlchemy.dialects.sqlite has been added explicitly
[FIX]GMO: for new facts with open dimensions, only really create them if thy do not exist yet.
They exist if they are c-equal (context equal) and if they have the same QName.