Improve dialogue highlighting

[vkbo]

Summary:

This PR:

• Splits dialogue highlighting from the selection of quote symbols.
• Adds a setting to highlight dialogue as either "None", "Single Quotes", "Double Quotes" or "Both",
• Adds a setting to allow open ended dialogue when highlighting.
• Adds a setting for narrator break symbols (single character).
• Adds a setting for opening characters for dialog lines (single character),
• Adds two settings for custom, alternate dialog symbols (max 4 characters each).
• Updates the syntax themes.

Related Issue(s):

Closes #1770 (allows two types of dialogue)
Closes #1771 (adds narrator break)

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