Add options for different behaviors in job assignment in server

When a worker asks for a job, the job server assigns the first job it finds when scanning the list of functions. This will add a behavior flag so that the job server can scan the entire list of functions it handles and choose the next job based on queue length and priority.

It may also be worth taking some time to explore other job assignment behavior options. Other behaviors to consider are ones based on time and round-robin with functions.