Fixing worker hashrates and activity status

* Fix hashrate calculations and include archived shares
* Fix worker activity to only check for our_result = Y shares
* Mark as active if worker has a hashrate > 0, removes a query

Addresses #561, crons need to be updated to remove the active flag from
as the worker activity and check the hashrate instead.
Fix IDLE worker detection

* Also mark as IDLE if no valid shares were received

Fixes #561
Merge pull request #576 from TheSerapher/issue-561

Issue 561