New todos:
- Show image of selected element separately from score when selection looks ambiguous,
- Join beam pieces (maybe can assume a beam section has no more than two pieces, but it could have more if there are consecutive rests within a beamed run),
- Some full beams are being detected as short beams.


- Stems on minims not found. Fixed.
- We have already detected staves before searching for most other stuff including beams and semibreve/minim rests. I'll make detection check that a rest hangs off or sits on a stave line before declaring it a rest. Done (and not prompting user for new element type fkn).