Implement a new PDS module for Wrangler that supports pods

[windley]

Wrangler modules add new functionality to Wrangler. See the subscriptions ruleset for an example.

We're doing this as a module because not all pico engine installations will have an associated pod server, so we want to be able to layer this functionality on.

Review old PDS implementations for ideas.

Requirements:

1. PDS is shared by all rulesets in the pico.
2. Exposes pod access control so that data can be ruleset specific if necessary.
3. Manages pico and pod as a pair when installed.
4. If no associated pod exists when installed, the PDS creates one for the pico.

[windley]

Some links on PDS:

1. https://www.windley.com/archives/2010/11/essential_characteristics_of_a_personal_data_store.shtml
2. https://www.windley.com/archives/2014/07/fuse_as_a_microservice_architecture.shtml
3. CloudOS PDS module (a169x676.prod)