Jobs Map Revamp

The jobs map no longer keeps a list of simulations for each user.
Instead, each simulation comprises an individual map entry with
its id as the key. This change speeds up job distribution considerably.

Simulation selectors were affected by the change and the order of
execution of simulations is no longer perfect.

Signed-off-by: Bennie Leonard <bennie.leonard@gmail.com>
Merge pull request #17 from benniel/jobs_map

Jobs Map Revamp