Batch endpoint does not restrict the max batch size

[hsiliev]

Batch endpoint does not enforce the max batch size and we can have different batch sizes from different clients.

The endpoint in router module does not use BATCH_SIZE. Still it might make use of MAX_INFLIGHT.

[cf-gitbot]

We have created an issue in Pivotal Tracker to manage this:

https://www.pivotaltracker.com/story/show/151755100

The labels on this github issue will be updated when the story is started.