Add a 'Create New' menu for documents in project tree context menu

[vkbo]

Summary:

This PR:

• Connects the already existing create document/folder actions in the "Add Item" menu of the Project Tree to a new submenu "Create New ..." in the context menu. No other code is needed, since the actions are already defined.
• Changes the label of the context menu "Transform" submenu to the same format as the other submenus.
• Fixes an issue with switching tab in Project Settings when opening it from the Project Tree context menu.

Related Issue(s):

Closes #1519

Reviewer's Checklist:

• The header of all files contain a reference to the repository license
• The overall test coverage is increased or remains the same as before
• All tests are passing
• All flake8 checks are passing and the style guide is followed
• Documentation (as docstrings) is complete and understandable
• Only files that have been actively changed are committed