Add limits for batch request size

[jcookems]

Dev Estimate: 8
Test Estimate: 3

The Service Bus docs say this:

Maximum message size: 256KB
Incoming messages that exceed these quotas will be rejected and an exception will be received by the calling code.

So, what if a user of SocketIO uses our module and tries to send a big message? Or if a lot of small messages get batched together to be a big single batch? Some thoughts:

1. If the batch is too big, split it up until it fits.
2. If an individual message is too big break it up until it fits.