Add capnproto serialization

[chetan51]

This is a super-issue to track progress.

• [ ] Add capnproto serialization to UnionTemporalPooler
• [ ] Add capnproto serialization to GeneralTemporalMemory
• [ ] Add capnproto serialization to TemporalPoolerRegion
• [ ] Add capnproto serialization to LanguageSensor region
• [ ] Add capnproto serialization to ClassificationModel

[subutai]

@chetan51 Please discuss with me before you start any of this work - thanks!

[scottpurdy]

There is also ClassificationModel and potentially other classes that require stored state in addition to the Network.

[chetan51]

@scottpurdy Added an issue for ClassificationModel. @BoltzmannBrain Any others?

[BoltzmannBrain]

LGTM