Matplotlib backend is not compatible with MPL 3.3.0

[M. Gronle]

The MPL backend of itom has to be adapted for MPL 3.3.0:

• The status bar is not officially supported any more
• _init_toolbar of navigation toolbar is not called from constructor any more. Call it directly.
• some changes in figureoptions dialog

‌

‌

[M. Gronle]

Here is a first fix to provide full MPL 3.3.0 compatibility

[M. Gronle]

fixes issue #130: The matplotlib backend is now compatible with Matplotlib <= 3.3.0.

→ <<cset 7ff897eb0a0c>>