Add random seed drops. Fix SQL mode detection.

- This only works for Official LongGrass currently (no custom blocks with
  base blocks of grass as to not break compatibility).
- Seeds have a 10% chance of a drop.
- If a seed is to be dropped, one seed is chosen at random from the
  registry and dropped. All seeds currently have equal chance.
Signed-off-by: Chris Sanders <zidane@outlook.com>