Rework some preprocessing functions, test jobdb implementation for preprocessing

[mmccrackan]

Work in progress. Sort of an update to #1156. Does the following:

1. Switches to per-group parallelization for preprocess_tod and multilayer_preprocess_tod.
2. Reworks preprocess_tod and multilayer_preprocess_tod to rely more on preproc_or_load_group since it does many of the same things.
3. Progress bar for preprocess_tod and multilayer_preprocess_tod.
4. Start adding jobdb support for both preprocess_tod and multilayer_preprocess_tod following similar implementation to record_qa.
5. Adds some standardized error messages in a class which can be input into a preprocessing error db.
6. Some more cleanup of functions and docstrings in preprocess_util.

Might split into multiple PRs if possible. Will need to adjust some things to make sure it doesn't break things downstream.