Change provider interface to separate "download" and "process" steps

[wagoodman]

When doing the initial port of all of the drivers, most of the drivers support a single entrypoint (fetch or refresh) which was rolled into the provider.Provider base class as update().

It would be more ideal to be able to split the operations of the provider into download() and process() to enable better local development and assurance that processing results will not incur network calls.