Allow components to be stored in sub-collections

[brettwillis]

Currently, components (repeatable) and dynamic zone are stored directly in the document. This does not provide good support for running queries on fields within those components.

• Add an option flattenComponents (global setting and per-model override) wich defaults to true current behaviour.
• On the per-model option, allow to specify a test for selecting which components are flattened.

When component flattening is disabled, store the components as individual documents within a sub-collection of the master document.

[brettwillis]

I have added indexing of repeatable and dynamic zone components, so querying is no supported (in a limited, preconfigured way).

I feel that the benefits currently outweigh the downsides of embedded components, so I'll close this enhancement for now.