Add underscore to dropoff

[br648]

Checklist

• [x] Appropriate branch selected (all PRs must first be merged to dev before they can be merged to master)
• [x] Any modified or new methods or classes have helpful JavaDoc and code is thoroughly commented
• [x] The description lists all applicable issues this PR seeks to resolve
• [x] The description lists any configuration setting(s) that differ from the default settings
• [x] All tests and CI builds passing

Description

Added an underscore to all occurences of start_pickup_dropoff_window and end_pickup_dropoff_window.

Front end PR for testing: https://github.com/ibi-group/datatools-ui/pull/952