Implement Appreciation DNA

[pospi]

Includes the Appreciation record type CRUD zome and associated indexes. Agreement would be a good blueprint to follow as this is a relatively simple record type.

There is an inherent assumption that Appreciation should be kept separately from Observation, which might turn out to be false. In this configuration, cross-organisational appreciations would require all organisations to share an Appreciation DNA in order to see the records. In some configurations it might actually be better to bundle Appreciation with Observation and mirror the data between collaboration spaces, similarly to how Satisfaction and Fulfillment are mirrored between Observation and Planning. In such a configuration, organisations could view appreciations from external orgs without having to share visibility into their coordination spaces.

Note however that the indexes on EconomicEvent (appreciationOf and appreciatedBy) must always be co-located with the events in Observation. So, this might behoove enough cross-organisational visibility on its own. More thought is needed, probably best to exercise this via integration tests and see what makes sense.

DEFAULT_VF_MODULES needs to be extended to have appreciation added to the whitelist in order for queries & resolvers for this module to show up.

Ideally, #85 & #40 would be completed before starting so that there is a well-established and vetted pattern in use; otherwise it's just more stuff to refactor later.