[UPDATE] Proper implementation of target bits

* [ADDED] New Config Option: Algorithm
 * scrypt and sha256d supported right now
 * might add SHA coin support across MPOS
 * Compatible with previous implementation
* [REMOVED] config option: pps_target
 * Replaced by config option: algorithm
 * Please update your config, defaults to srypt now!
* [ADDED] Unpaid Shares in Dashboard
* [MODIFIED] User estshares from DB query instead template math