Avoid Leaflet "L" from leaking into global
Create dist if it doesn't exist and uglifyify by default
Serve hubmap embed assets from /embed and rename /hubmap to /maps

Previously the assets required to embed a map where in
/static/hubmap/dist/ they are now simply in /embed/. The main JS file
hubmap.js is a template so that the base URL for the server can be
easily included.
Update initial view to be centred on Surrey County