Indicators configuration

This adds models to store the transit indicators configuration based on the wireframes (I checked the functional spec as well but wasn't able to find any others). The configuration includes:
- local poverty line
- buffer distance
- maximum allowable commute time
- maximum allowable walk time (these last two are for the job indicators travelshed).
In addition, peak travel times exist as a separate model since there could be more than one of them.
I wasn't sure about this and I think we probably need some guidance on this. I definitely think that people might want to input it in their local currency, but it has also been my experience that at least in developing countries, people tend to have a pretty good sense of the USD<->local currency exchange rate because USD are used for international transactions and sometimes as a hedge against local currency fluctuations.  There also might be reasons (e.g. sharing indicators across cities) why we might want to store everything in one common currency and convert in the UI, but then we'd need to add an extra field for the local<->USD conversion.