Show historical feed availability visualization based on HTTP success/failures

[barbeau]

Summary:

This is related to the rule of a minimum HTTP request success rate (https://github.com/CUTR-at-USF/gtfs-realtime-validator/issues/113) as well as logging connection failures as errors (https://github.com/CUTR-at-USF/gtfs-realtime-validator/issues/278).

It would be nice to have some type of visualization (e.g., a graph) showing the historical feed availability based on HTTP requests that have succeeded or failed. This would help troubleshoot issues like the one discussed at https://groups.google.com/forum/#!topic/onebusaway-developers/8BFb-r5rs4I where it's not clear if the GTFS-realtime feed is having intermittent issues or if it's a problem with a different consuming application. It would also be good to annotate this graph for each request showing the HTTP failure code (e.g., 404).

Steps to reproduce:

1. Start the webapp
2. Monitor a feed

Expected behavior:

Give me some visualization (e.g., a graph) showing the HTTP failures and successes for each request over various time scales (e.g., hours, days, weeks).

Observed behavior:

You can't see visualize how often a feed has failed to return a valid GTFS-realtime response.

Platform:

N/A