Collapse hierarchy does not check pre-conditions

[seyyedaliayati]

Describe the bug
For collapse hierarchy it's required to make sure about input classes. You can look at here for more details about this refactoring

To Reproduce
Steps to reproduce the behavior:

1. Go to 'refactorings/collapse_hierarchy.py'
2. Run the script on your test project
3. See error

Expected behavior
As an example if A does no extends B we should check that before beginning the process!