M3DB Schema Management

[Haijuncao]

This issue propose to add schema management to M3DB as part of M3DB's effort to support complex type values.

The proposal will discuss schema definition language, schema evolution, storage, deployment, developer/client interaction. It also details dbnode schema in memory propagation into schema aware encoding library (proto encoder/iterator).

https://docs.google.com/document/d/1h0eYFCpXQykqXlAXpQFMxiV5TJRKI6d8bSLuY5u9WIo/edit#heading=h.b8fywakslp97