Specifically the cache and dataset needed for max mode mining.

But use shared keys for caches and datasets. We use the key for local
caching of the vms but this key is also passed to the cache naming. We
need our cache to be unique but caches to be the shared.

Make sure the seed hash is checked and updated when needed. Ensure the
block template is updated when needed.

- Moves the stats incrementer to cache a number of counts and write
  later instead of on each cycle
- Starts a thread to watch the block template and notify the thread when
  it changes