Combine metadata queries for unified UI

[abbiemery]

We currently have different metadata graphql queries for each of the tiled data types. As part of the interface discussion we should look at how to combine these.

[tpoliaw]

Was this referring to the meta: Value field on most types or the data returned by api/v1/metadata/{path}. Using the new node::NodeAttributes enum and the change to make responses generic as part of #89, metadata can be retrieved into a single instance of the metadata that would be retrieved in the data: Vec<Data> entry by searching the parent container. Is that enough to handle any metadata we need for the time being?