Streamline process for loading python CompassApp

[nreinicke]

Our current workflow for building an OSM based RouteE Compass app is to create a new osmnx networkx graph and then convert that into our file formats, saving everything into a folder that later gets loaded as a CompassApp object. We could offer a streamlined option that goes straight from a primitive into a fully loaded compass app, something like:

app = CompassApp.from_place("Denver, Colorado")

app = CompassApp.from_polygon(some_shapely_polygon)

Where, under the hood we call the respective osmnx methods to build the networkx graph, cache all the necessary files and then load the application from the resulting files. Maybe we could use the osmnx.cache_folder location to store the files for the application.

[zenon18]

zenon18 (Mark W.) will like to work on this issue

[nreinicke]

Closed by #225