Case insensitive tags

[vkbo]

Summary:

This PR changes the logic of the index class to capture the name of the tag with case preserved and save it as a "name" value in the tags index, and then converts it to lower case for usage in the references index itself. When a request is made to list all references in a document, the name is looked up in the tags index, and the original display name restored.

The extra lookup could be a small delay in very large and complex projects, but it's the only way to achieve this.

The changes to support this feature is kept entirely inside the index class, but it does require an index rebuild since the old index will be invalidated by the changes.

This PR also cleans up annotations in the Outline module.

Related Issue(s):

Closes #1313

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