Update icons

[vkbo]

Summary:

This PR removes a bunch of unused icons, and adds an icon for Novel Section documents. It also replaces the header icons on the Project Details dialog with the header decorators. This was the last place the header icons were in use, so they too have been removed.

Related Issue(s):

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