Add a context menu entry to set item name from heading

[vkbo]

Summary:

This PR:

• Changes some of the logic in editor and viewer to use proper signals to communicate with other components.
• Cleans up the enums in the editor and viewer.
• Adds a context menu entry in the editor to rename a document from a heading in the text.
• Adds test coverage of the context menu.

Related Issue(s):

Closes #1503

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