Adding `parse_model_key_file` function to `parsing`
Updating `ABCTeam` class.

Moving call to `_parse_observed_paths()` method from `__init__`
to `run`, so that an instance can be created before the observed
data paths are populated.

Also, updating `_parse_previous_prior_dir` method to also find
and parse previous config info in the "model-key.txt" file.
Updating `dmc.py` script.

Creating `ABCTeam` instance before generating observed summary stats to
allow more complete and consistent information logging.

Also, adding `--dry-run` option to allow processing of settings and
generation of information logging, but without running any analyses.