Minor improvements for 2.6 beta release

[vkbo]

Summary:

This PR:

• Makes some improvements to the dialogue settings text in Preferences.
• Moves the replacement of alternative apostrophe and horizontal bar Unicode symbols to later in the tokenization process. They are both available to prevent the dialogue highlighting from misunderstanding apostrophes and em-dashes, but now that dialogue highlighting is also processed in the viewer and manuscript build, they most be replaced after dialogue is detected, not before.

Related Issue(s):

Comment: #1773 (comment)

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