Add an ignore text format and allow multi-paragraph formatting

[vkbo]

Summary:

This PR adds a new block format, that is a variation of a comment which uses %~ as a prefix instead of a plain %. It only has a minor difference in that it can be used to ignore text paragraphs without having to pollute comments if comments are actively used in the text and draft manuscripts for labelling plot progression and so on. The %~ will completely ignore the lines when building a manuscript, also when comments are included.

Using it is completely optional, and for those who need this distinction. It has been given the keyboard shortcut Ctrl+Shift+D which is related to the strikeout shortcut Ctrl+D.

In addition, this PR adds support for applying/toggling formats to more than one paragraph.

Related Issue(s):

Closes #1075
Closes #1042
Closes #1687

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