Add ResqueQueues plugin

The ResqueStats plugin reports pending jobs across all queues, which can
be useful by itself. However, it doesn't give much insight into which
queues are particularly far behind.

This plugin tries to change that, by looking at all the queues, and
reporting the sizes back.

This will almost definitely run into problems once you hit 20 queues,
but can be addressed then (either specify which queues to monitor, or
only do top 20).