change python3.8 only debug f-string to compatible

Pushes version, updates changelogs, adds py3.9 to pyproject.toml

Forces correct config value for [programs] vdub

Fixes error cutting HD2 files

Fixes problems with new HD format

* otrverwaltung3p/GeneratorTask.py
  - GObject.idle_add -> GLib.idle_add

* otrverwaltung3p/gui/CutinterfaceDialog.py
  - self.filename is now a Path-Object, passed to functions as string
  - Reorders and groups event functions
  - Adds seconds display to frame-time info string
  - Adds function on_btn_test_next_marker_clicked()
  - Adds function on_btn_test_cut_clicked()
  - Adds button to open settings
  - Adds label under cutslistview showing the resulting length of the cut video

* otrverwaltung3p/gui/LoadCutDialog.py -> Cutinterface
  - Adds third stage of cutlist search: by size

* otrverwaltung3p/actions/cut.py
  - Simplified detection of codec_core

* data/plugins/Mkv.py
  - Makes icon sizeable

* data/ui/CutinterfaceDialog.glade
  - Adds new label lbl_duration_cut
  - Adds new button btn_test_next_marker
  - Adds new button btn_test_cut

* data/ui/PreferencesWindow.glade
  - Sets movieWindow max size to 2560x1440

* data/ui/ConclusionDialog.glade
  - label_cut_status wraps word

* otrverwaltung3p/cutlists.py
  - cutlist.upload now uses 'requests' lib

Fixes HD videos are cut with wrong encoding parameters

Cut video will not be moved to archive if cut was cancelled (conclusions.py)
Fixes bug in fileoperations.py
and maybe more

New version 1.0.0b6

Pushes version to 1.0.0b5

Silence some debug messages

Fix bug in fileoperations:make_unique_filename

Use package 'appdirs' instead of 'xdg' (path.py)