Merged with default branch to prepare a new release. maintenance release-20.07

PipPackagesWidget: made the cache actions dependent on pip version of selected environment. changed the order of packages in 'install_requires'. Hopefully this install pip and wheel before PyQt5.

Removed some more Python2 related code.

Updated Russian translations.

Removed some more Python2 related code.

Utilities: fixed an issue determining the tools path for pyside2.

Removed support for Python2 and removed support for Qt4 (PyQt4 and pyside).

QtHelpDocumentationSelectionDialog: changed code to support adding complete categories by just selecting the category title.

Corrected an entry on the Application config page.

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eric ide