Assorted UI tweaks

[tjvr]

I don't even remember what half of these mean any more.

The "misc" section of my to-do list, lets say

• [ ] disallow saving when invalid vars
• [ ] "define" validation
  • error if bad procedure argument names
  • validate procedure words
  • check custom procedure arguments must be parenthesised!
• [ ] revisit number literal color: darker?
• [ ] .new-variable background saturation
• [ ] touching the drag button pushes a null op onto oops stack
• [ ] ambiguity
  • create clone of ""
  • point towards ""
• [ ] number literals 0001010
• [ ] parse numbers in blockArgs, rather than when processing number literals
• [ ] cmd+return in NamesEditor [mac]
• [ ] precedence of mod
• [ ] renaming sprites doesn't update code refs
• [ ] renaming variables/lists doesn't update code refs
• [ ] display/set currentCostumeIndex ; +when rearranging