Allow launching multiple tasks per resource offer

Mesos allows frameworks to respond to offers with a list of tasks to run.

Currently, Chronos launches at most task per offer. I think it would be helpful to respond with many tasks from the queue per offer to reduce the delay between getting added to the queue and being launched on Mesos.

This patch accomplishes this in a simple way by repeatedly popping tasks from the queue as long as there are resources remaining to satisfy them, and then launches them all together.
The idea is to use all offers up, so I think that the order in which we fill offers less important as long as there are enough queue tasks to fill the offers up. If there aren't enough tasks, then I believe that the order the offers are used could be important for some use cases, but I couldn't of anything compelling from my own setup. I'm happy to put it back in if it is important to others. I also didn't understand why the sorting was done for resources reserved for roles that aren't "*" as opposed to resources reserved for config.mesosRole().