Feature/refactor params

This merge request refactors the use of parameters to allow fetching of parameters from the database in addition to only calculating derived parameters (stops buffers, road length, etc.) once so that multiple indicators that need access to these parameters will not be recalculating these values.
@lossyrob - This indicator only needs params.settings, yet because the type is IndicatorParams, I believe it also has access to  StopBuffers, Boundaries, and RoadLength. Some other indicators effectively narrow down the params that are passed in, e.g. CoverageRatioStopsBuffer, which is limited to only StopBuffers and Boundaries -- no RoadLength (or, I believe, settings). I think what we'd really want to use here would be another type that only gives us access to params.settings. Can you think of a way to allow for this?