Namespace memory image

[johnny-morrice]

We currently support a fast memory image for indices.

Decoupling the application state from IPFS allows us to perform joins (write queries) in parallel.

However, we still always write to IPFS for the namespaces.

Whether or not the namespace (and its index) will be written to IPFS should be controlled by a flag on api.Request. If the namespace will be directly written to IPFS, the path to an index for that namespace should be returned to the user. Otherwise, the namespace will remain cached until a write during the application pulse.