[Data] Update schedule configuration

[lauriemerrell]

The way we have to load the schedule data is a little arcane, because we have to handle the concept of "when was this online".

I think we need to do the following:

• Create a schedule_config.yml file to store information about schedule versions (replacing the dictionary here)
• Write up information about how we use schedule data in our data analysis README and/or our actual website methodology section

Here's an explanation I sent to @dcjohnson24 offline about how the schedule config dictionary is constructed:

The version uploaded on June 3 takes effect on June 4 because I don't know what time of day it should become effective
And then that June 3 version ends on June 7 because there's a new version uploaded June 8
It's just non-overlapping ranges showing when that version was online, no reference to actual feed content

Sidebar I think we may have some slight weirdness about these dates because I think that the dates on TransitFeeds are in UTC time and our work is all in Central Time.

[dcjohnson24]

Thanks for this. I've made an attempt at scraping the schedule versions from TransitFeeds here. I can work on adding the explanation of the schedule dictionary construction to the README and website copy.