Generate Riak Search schema from Document metadata

Detect Documents that have search indexing enabled
Allow annotation of properties that should be indexed in Search
Generate Search-compatible schema from Document metadata
- Option to ignore unknown fields, or accept without additional type information
Either:
- Rake task to apply Search schemas via search-cmd (useful in deployment as well)
- Automatic fetch/comparison/update of stored schema via a client interface (TBD)

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