Improve icons throughout

[David Aspinall <da+pgtrac@…>]

We need more icons and improved existing ones. Generally icons should be smaller and less obtrusive.

• Document icon for proof scripts: can be PG star on a document
• Improved outline icons: should have uniform sizes, be more "proof-oriented" (e.g. turnstile for open goal, qed blob for close goal, instead of open and close doors!)
• Also needed: separate icons for:
  • proof project (maybe provers can override this)
  • symbol editor

[David Aspinall]

Milestone PG-Eclipse-1.1.0 deleted