[bug] get rid of all default seeds in different configuration sources
There are currently 3 "seed" options:
- A "seed" for simulations
- A "seed" for preprocessing (this mostly controls randomization of dataset splits)
- A "seed" for training
All of these had default values in the default config files. I think partly as an artifact of when I ported over some of Jean and Theophile's old config files into the code.
In practice, users should expect stochasticity by default. The schemas have a default value of "null" for all these seeds, which is equivalent to random seeding of the PNRG. If users want to set a specific seed for reproducibility they should do so manually.
(Possible future enhancement: Record the seed that was used so they can reproduce the same run even if the seed was not set explicitly first.)
Fixes (?) #109.