Da Bubbles

Python side
* Make the lat/lon in the pre-rendered geojson doubles (instead of strings). This makes it so that, when they are rendered, they don't need to be converted to floats
* Also include total # of houses in the hmda api

JS side
* Most heavy lifting is around reworking a few functions to account for *multiple* layers/data sources
* Url param parser to fetch lender id
* Expanded `draw` function to draw circles (if rendering the loanVolume layer)
* When rolling over bubble, show metrics in the left-bottom corner (as we do with tracts)
As a readability thing, can we label this makeBubble instead of mkBubble?