Merge url and URLFetcher into ConfigFetcher?

[ssawchenko]

It seems redundant to have a URL and then also an interface that assumes we use that URL to fetch the data. For apps that already have some form of config fetching being done it may be more robust to have a ConfigFetcher interface and have the DefaultNetworkFetcher take in the URL directly instead. Apps that pull the config file elsewhere can implement that interface, and apps that want to make the URL call directly can use DefaultNetworkFetcher.