Enhancements for LocationChoiceModel

Added several configuration options:

- location_id_col: name of a column in the choosers table.
  If this option is given the choosers table will be filtered
  to include only rows for which this column is nan.
- choosers_fit_filters and choosers_predict_filters:
  For filtering the choosers table before model fit and prediction.
- interaction_predict_filters: For filtering the choosers/alternatives
  merged interaction table after the merge. Useful when it's necessary
  to filter based on comparisons of chooser and alternative properties.

In addition to the new options I changed the order of the arguments to
MNLLocationChoice so that all the filters can be optional.