Alternate data hierarchy for validation parameters/members

[sgsmob]

The validation code expects a long list (>15) of parameters to be set in the params.json file and then copied over to members of the Validator class. This not only makes the Validator class fail linting but also is hard to reason about. We should refactor both the structure of the params.json file as well as the members of Validator to be hierarchical rather than flat, i.e.:

{
  "date_options": {
    "start":  ...
    "end":  ...
  }
  "single_file_options": {
    "min_sample_size": ...  
  }
  "signal_options": {
    "lag": ...
  }
}