Additional denser_bart features

[scoobmx]

1. Generate station selector field from API key field
2. Add a toggle for a visual mode that graphs departure times instead of using text marquees. This allows station abbreviations to be 3 letters instead of 2.

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[scoobmx]

@matslina i'm seeing 2 issues and i'm not sure if they are fixable.

1. On the schema page, the generated field doesn't show up until the user puts something into the source field. I have the source field set to "" by default, which is supposed to produce a generated field anyway, but for now I have to first input some garbage, then set it back to "" to see the generated field.
2. On the schema page, often it will show no data, even though the actual app on the device will work fine, and I'm not sure if this has something to do with caching. I don't think it has to do with the generated fields since it was like this even before I implemented that.