Standardize status responses to the client

[dmfenton]

@ngoldman This could use a solid read. I'm going to hold off on adding a lot of tests around the new download method until I refactor it further into more methods.

This PR begins to refactor the massive findItemData method and moves all status returns to a single method called _returnStatus

Some key points:

• we will always return 502 if there was an error emanating from AGOL, or a Feature Service
• we will have a consistent structure returned to clients in the payload of any error -> the structure kinda sucks but flattening it would be a breaking change so I'm going to hold off
• resources will either have a status of processing or failed, this allows us to add logic later to keep things in a failed state for a controllable amount of time
• feature service logic in getFeatureServiceInfo has been replaced with methods in Featureservice.js

[ungoldman]

Generally looks okay to me.

As an aside, I think we should start moving methods out of the controller if they don't correspond to routes. Typically any exposed method on a controller should correspond 1:1 with a route or at least a route filter in express/MVC. Moving utility methods into a lib/ folder would take down the rather long line count here too.

[dmfenton]

Totally agree that we should factor out methods that don't correspond to routes. Good point about the utility methods.

[dmfenton]

@ngoldman good to go