Rewrite checking for updates

[vkbo]

Summary:

This PR drops the old "Check for Updates" dialog box in favour of a widget that can be included in other dialogs. The widget has one line of current version information and a link to the Releases page of the website, and a second line that by default says "Latest Version: Check Now" where clicking "Check Now" will retrieve this information from the GitHub API. The API call is rate limited to 60 calls per hour, which should be fine since the widget will only let you click the link once.

This new version info widget is added to the Welcome dialog and the About dialog.

Screencast.from.2024-02-14.19-01-40.mp4

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