Fix the link to the Qt project page. Also link to their page for license
information instead of pointing at a non-existant file in our
repository. This fixed issue #5.
Mention the Silk icon set in the about dialog and link to its page. This
should also make the hard-to-find CREDITS file dispensable.
Generally redesign the about dialog to use layouts for its design.
Rename the files and classes for the dialogs to share all the same
naming pattern. This should make navigation in the code a bit easier.
Do not include dialogs not rewritten yet; they'll be edited as they are
redesigned.