Search on git.duniter.org, can be set in constants.py

Update and cleanup README.md

Fix blank window displayed if no current connection

See https://appimage-builder.readthedocs.io/en/latest/intro/install.html#install-in-a-docker-container

Image weight is smaller
Image include wget to build AppImage
Python >= 3.6.10 requirement is now the default

https://github.com/harvimt/quamash/issues/123

reformat code and tests

bug in pylupdate5 in PyQT5, see: https://github.com/pyqt/python-qt5/issues/54

bug in pylupdate5 in PyQT5, see: https://github.com/pyqt/python-qt5/issues/54

[fix] #802 fix ""Send as source" not displayed in context menu on standard condition received transaction

Add test on parse_transaction_doc()