Improve GUI scaling

[vkbo]

Summary:

This PR restructures how icons and buttons are created and fixes a number of issues where icons and buttons did not scale with GUI font size. The intention is that all buttons and icons should be relative to the selected GUI font size. This was mostly the case, but not everywhere. This PR also moves some of the calculations into helper classes to reduce code repetition where buttons and icons are added.

Related Issue(s):

Closes #1787

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