Extend heading styling options

[vkbo]

Summary:

This PR makes the following Manuscript Build changes:

• Adds a set of centre and page break switches also to top level titles.
• Generalises the "ODT Documents" section to "Document Options".
• Changes the colour switch option to only apply to headings (this will be needed in the future)
• Adds a switch to disable font scaling of headings, meaning they're the same size as the text.
• Adds a switch to toggle bold font weight on headings.
• The "Document Options" switches also apply to the preview.

Other changes:

• All output format classes have been moved out of core and into a new formats folder.
• The test have been restructured accordingly.

Related Issue(s):

Closes #2023

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