Display distance and time estimates for routes

[jeancochrane]

Overview

Use the combined length of the route fragments in meters to display a distance and time estimate when a user searches for a route.

Closes #27.

Demo

Testing instructions

• Ensure tests pass on CI
• If you don't already have a development environment set up, let me know and I'll get you a dump of the database and help you restore it
• Start the development server: docker-compose up --build
• Navigate to http://localhost:8000/
• Enter a route and confirm you see a distance and time estimate display in the search box
• Search for another route and confirm the distance and time estimate changes
• Hit "Reset search" and confirm that it clears the distance and time estimate

[jeancochrane]

Overall I like this, but I recreated a few routes in google maps for comparison and got pretty different results for distances (e.g. from pilsen to washington park google said 8.4 miles and mbm said 6.4). Any idea what might be causing that?

I appreciate this thoroughness! I'm not immediately sure where the error is but the part I'm most uncertain about is how the length_m column is being generated. I'm going to do some digging this weekend and see if I can surface the source of the discrepancy.

[jeancochrane]

I finally got to the bottom of the incorrect length calculation! The details: it turns out I had forgotten to use DISTINCT when joining the route fragments to the MellowRoute table in the get_route() query, which created duplicate segments in the output in cases where one OSM ID was used for more than one MellowRoute (pretty common at the edges of neighborhoods, where the bounding box of one neighborhood often overlaps with another in the route marking interface).

Want to double check to make sure that the routes you tested show the correct distance now @kalilsn?