Refactor tasks and services to accept only options with URL

[patrickarlt]

I had a conversation with @jgravois about this today so I will attempt to transcribe the notes here.

Initializing Tasks and Services with the (url, options) pattern is starting to cause problems that look like horrible kludges in downstream plugins like the geocoder.

This proposed code by @jgravois is pretty indicative of the problem. https://github.com/jgravois/esri-leaflet-geocoder/blob/empty-constructor/src/Tasks/Geocode.js#L28-L41. That code has to check for:

1. passing a Service as the first param,
2. passing url and options
3. passing options and using the default URL

In short we shouldn't have to write code like this. Its much cleaner to make url an option that can be passed in. This means that the first parameter is always either

1. an options object with url, or no url to use a default URL
2. a service, in which case we only need to check for the presence of request and switch accordingly

This is a major breaking change but we are still in a release candidate stage of Esri Leaflet now is the time to do this to simplify downstream plugins that want to use a default for URL.

[jgravois]

resolved by #432