Fix #6661 gui updates

[mkeilman]

A handful of updates (not everything in the gui-experiments branch):

• Bolder dark gray panel titles. There was some discussion of using blue, but in any case they should be readily distinguishable from clickable elements
• "Save Changes" is now "Save"
• "Action buttons" used to move, copy etc. items in a list are a darker blue. Implemented only for radia at the moment; they should live in a directive or class for general use
• Supporting changes in the css including trying out custom properties

Suggestions encouraged!

[moellep]

Two things I notice:

• The "Save" button is now too small, smaller than the cancel button. Adding a style like: "min-width: 7em" would help.
• The formatting applied to the panel headings should also be applied to the modal dialog headings.