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.
Sure, there'd just be a trait that means, 'I have a settings value', just like how StopBuffers means 'I have stopbuffer methods'. 

Or, you can convert the IndicatorSettings into a trait, and have the object initialize a `new IndicatorSettings { ... }` trait like the rest of them do.