Support for update traits mutation

[appaquet]

Right now we need to update a trait as whole, leading in inefficiency at network and storage level. Unfortunately, we can't support indexation of update traits mutation since the mutation may not contain one of the indexed field.

We could eventually fetch all traits of an entity at index time, but this would hit indexing performance. The intermediary solution is to do it when we receive the update mutation and generate a second mutation with whole trait. This isn't helping on storage bloating, but compaction will help resolve this issue.

See #212 for compaction of mutations