Allow to choose which blocks have SE units

[Tilps]

Inspired by testing which suggests a 15 block net only needs 3 SE units to get the same loss values.

[Tilps]

yaml options.
No se_blocks section means same as before, all blocks have SE.
se_blocks: [] means no SE at all.

se_blocks:
  - 1 based block numbers
  - listed here
  - to control exactly which