Send vertex label to user log processor for all mutations

[porunov]

Right now using LogProcessorFramework there is no way to retrieve mutated vertex label. Because messages don't include vertex label but only vertex id.
This is a blocker for #3155 .
Without sending vertex label id in the mutation message we won't have vertex label information during log processing.
I.e. vertexLabel() method will always return default vertex label for all received vertices (unless this particular vertex was cached on the receiving instance, which usually isn't the case).
Without knowing vertex label of the mutated vertex we won't be able to properly invalidate indices which are bound to specific vertex label. I.e., those indices which use indexOnly(JanusGraphSchemaType schemaType) method.
To be able to invalidate those indices (necessary for #3155) we should provide vertex label information.

Describe the feature:
Provide vertex label information for mutated vertices in log processor.

Describe a specific use case for the feature:
Implementing global db-cache invalidation feature (#3155).

[porunov]

The issue is obsolete because we are able to invalidate cached indexes without knowing vertex label as stated here: #3264 (comment)

Thus, closing this issue.