add arguments to pipeline model steps to make module reuse easier

[bstabler]

In order to more easily reuse model components, we plan to add to the pipeliner the ability to read an optional dictionary of arguments for each step. This has lots of uses and means the pipeline acts somewhat like DOS or Bash as well. The arguments are optional and often just one "general config type" argument is passed, which is consumed by a method that does further configuration - such as get the appropriate expressions file for the model type. To better illustrate the idea, here is a partially re-imagined model list:

_MODELS = [
  'compute_accessibility',
  'location_sample, TYPE='school',
  'location_logsums', TYPE='school',
  'location_simulate', TYPE='school',
  'location_sample', TYPE='workplace',
  'location_logsums', TYPE='workplace',
  'location_simulate', TYPE='workplace',
  'auto_ownership_simulate',
  'cdap_simulate',
  'mandatory_tour_frequency',
  'mandatory_tour_scheduling',
  'non_mandatory_tour_frequency',
  'location_sample', TYPE='non_mandatory_tour',
  'location_logsums', TYPE='non_mandatory_tour',
  'location_simulate', TYPE='non_mandatory_tour',
  'non_mandatory_tour_scheduling',
  'location_sample, TYPE='atwork_subtour',
  'location_logsums', TYPE='atwork_subtour',
  'location_simulate', TYPE='atwork_subtour',
  'mode_choice_simulate', TYPE='tour',
  'create_simple_trips',
  'mode_choice_simulate,' TYPE='trip'
]