Decorator fixes

[David Aspinall <da+pgtrac@…>]

• Decorator icons should be improved: make them smaller.

• There are some cases when the decorators do not get updated to reflect the active script changing. These should be tracked down and fixed. The failures may be related to recent changes in ProofScriptDocument.java which calls a method to update them; perhaps that method should be called in more places now.

[Graham Dutton]

Other decoration possibilities:

• decoration should become blue when fully processed, even when active (?)
• decoration should become 'unset' when fully unprocessed, even when active (?)
• Decoration should distinguish between active & processed (blue) and processed & not active (dark blue) (?)