Summary:

This PR greatly simplifies the About dialog:

• The big blob of text with license info on the first tab has been removed, and replaced by a link to the license, and the License tab has been removed.
• The release notes tab has also been removed, and instead there is a link to the release not DNS alias for novelwriter.io. It forwards to the current releases page at any given time.
• The credits page has been kept as-is and is the only text box left. It occupies most of the dialog.
• The logo, app name, and version information has the same layout as on the Welcome dialog,
• When the user updates or first installs a version of novelWriter, a regular Info box pops up and says which version has been installed and links to the releases DNS alias.
• A credits entry has been added for the new artwork.

This PR brings the design of the About dialog in line with the other dialogs and tools.

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