Add Paths and Folders to Catalogue TreeView

[pboettch]

Addresses #59

[jeandet]

While testing I got one issue when trying to drag a folder inside a folder:

Traceback (most recent call last):
  File "/var/home/jeandet/Documents/prog/tscat_gui/tscat_gui/__init__.py", line 497, in _external_signal_emission_changed
    if isinstance(action.entities[0], _Catalogue):
                  ~~~~~~~~~~~~~~~^^^
IndexError: list index out of range

[pboettch]

While testing I got one issue when trying to drag a folder inside a folder:

Traceback (most recent call last):
  File "/var/home/jeandet/Documents/prog/tscat_gui/tscat_gui/__init__.py", line 497, in _external_signal_emission_changed
    if isinstance(action.entities[0], _Catalogue):
                  ~~~~~~~~~~~~~~~^^^
IndexError: list index out of range

This is fixed, but I have a new problem, maybe related to a newer Pyside6 version and unrelated to folders/paths: 176b8fa

[jeandet]

Doesn't crash anymore but folder drag and drop doesn't work. It should either work or acceptDrop should return false for folders.
The former is preferable since crating a folder in the right position isn't that intuitive and trivial for new users.

[pboettch]

OK, I agree.

When dropping a folder the full folder-structures (with subfolders and its catalogues) will be moved and/or created.

I think they should be deleted from their previous/dragged position. What do you think?

However, moving a folder is not undoable, except for moving it back manually. Or when there was a catalogue inside, this is undoable.