Merge pull request #418 from raistlinthewiz/develop

hashrate calculation fix, job-tracker improvements
Merge pull request #419 from raistlinthewiz/develop

v0.1.5 PR
Added an error handler to pool initialization methods so we don't get chipered error messages any more in-case a pool can't initialize.
Pools whom can't be initialized will be not added to PoolManager's internal storage now.