Feature/better external data

[jthrilly]

Resolves #885

• Allows external data that uses variable names rather than UUIDs to be imported, and makes a "best guess" at converting them to UUIDs on import.
• Variables that cannot be mapped to the codebook are left unchanged
• Allows CSV files to be specified as external network data, and converts them to network JSON when loaded.

[jthrilly]

This needs to be tested on cordova before merging. Load development protocol from settings to do this.

[wwqrd]

Already acknowledged with @jthrilly, csv isn't working for cordova (ios + android).

[jthrilly]

In response to the poor performance of this, I made a stab at moving it to a web worker. The long term idea would be to move all blocking code to workers.

It has definitely helped, but not as much as I had hoped.

I think this means that the long, long term solution is to calculate this data once at a non performance critical moment (such as starting an interview session, or when the protocol is installed), and then store the decoded and restructured data. Then, stream it in as we do with media assets.

[wwqrd]

I think it would be great to have this generate at interview start.

Do we have any way of determining which bits are slow? If it's due to having large files/objects in memory then we may need to think of more alternative approaches, like a restful api, since we can't stream json.