Merge pull request #1402 from Corvalius/master

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Merge pull request #1403 from Corvalius/master

RavenDB-2681
Avoid unnecessary allocations
Prevent recursive transformers
Don't attempt to serialize the cancellation token, no point
Exposing score explanation to stats
Avoiding allocations if we don't have to
RavenDB-2638 Show indexing perf graph per index
RavenDB-2638 Show indexing perf graph per index
Adding passing test