Add a Trait Type model and db table

The event api will provide a way to list all trait types for
a given event type. The current data model does not provide
an efficient way to get all trait types.

This change introduces a trait_type table, and TraitType model.
Trait information can be retrieved with this simple query into
TraitType:

SELECT id, desc, dtype FROM  trait_type;

The UniqueName table is no longer needed, so it has been removed.

Partial-Bug: 1211015
Change-Id: I6ec29dc1d71b5590204d7e7b1bf121c2c1ca1904
Merge "Add a Trait Type model and db table"