Export Project Summary Improvements

[cycomachead]

Well, some of these could have been done years ago, if only we knew...

Lots of graders complain about scrolling too many pages. This makes some sense.

Simple things:

• [ ] Remove the URL from the top
• [ ] more clearly identify 'Project Notes' as what it is.
• [ ] Consider moving Snap! towards the top, and possibly adding the date.
• [ ] We should sort the scripts ABOVE the costumes / sounds lists for each sprite.
• [ ] Add next/prev links to the bottom of each code section.
• [ ] filter out blocks hidden by libraries, or hidden in the palette (if custom).

Harder ideas:

• [ ] Make the PDF output be text-searchable. (and write a comment letting readers know cmd-f works)
• [ ] include summary stats like the count of various blocks used?
• [ ] allow excluding all library blocks.
• [ ] create an "condensed" view of the blocks display. This would mean rendering with different visibility settings than default. (Flat mode? Fade blocks 100? 50?)