Move the help into a separate class.

Also move the dialog classes into a new directory.
The last tab of the help dialog is orphaned so far (it mostly dupes
the about dialog).
Parent help dialog to main window.

Also restore the default look for QTextBrowser, because no frame/background
just looks wrong.
Add icons to menus and windows.
Use the previously orphaned about text to make a better About dialog.
Put the commit hash in the version number.
Merge branch 'helpdialog'