UI usability fixes

[vkbo]

Summary:

This PR:

• Removes the 2 px margin on the sidebar.
• Changes when the editor auto-completer is triggered to only be activated on single keypresses (add or delete) and nothing else. It was triggering on other document change events that were not user-initiated, like during loading of a document when the cursor had last been positioned at a tag/reference line.
• Changes the auto-replace feature to also run on keywords again. It has accidentally been disabled on such lines.

Related Issue(s):

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