Allow hiding scene and section titles in export builds

[vkbo]

Summary:

This change adds a "Hide scene" and "Hide section" switch to the Build Novel Project tool. The support for this was already in the export tool, but not connected to the Build GUI.

Related Issue(s):

Resolves #972

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