2164 cancel button python gui

[JoKurth]

No description provided.

[JoKurth]

This branch is based on #2162 .

current status:
Conceptually, everything should work. But there is a bug that needs to be fixed:
When starting a proof the following error occurs and the program crashes.

[2024-08-14 19:29:22.083] [ WARNING ] [hetsgui.windows.ProveWindow] Proving at node ToProve failed for goal this_is_incorrect: Traceback (most recent call last):
  File "/usr/local/lib/python3.10/dist-packages/hetsgui/windows/ProveWindow.py", line 162, in prove_goal
    self.node.prove(prover, comorphism, include_theorems, [g], axioms, timeout)
  File "/usr/local/lib/python3.10/dist-packages/hets/DevGraphNode.py", line 91, in prove
    threadId = apnR[0]
  File "/usr/local/lib/python3.10/dist-packages/hyphen/marshall_ctor.py", line 341, in tuple_getitem
    return self._components[idx]
AttributeError: '(,)' object has no attribute '_components'

Additionally, when opening a file to prove the following warning is printed multiple times:

(hets:7): dconf-WARNING **: 19:29:05.866: failed to commit changes to dconf: Failed to execute child process “dbus-launch” (No such file or directory)

This is especially interesting as I did not change any code that should be involved in the choosing process.

Functionality for aborting conservativity check or consistency check is not implemented.

@b-gehrke Maybe you can take a look at it.