Adding working user admin panel to query user DB

* Users are all fetched from the DB
* Each user is assigned special stats
 * Hashrate
 * Shares
 * Balance
 * Est. Payout
 * Est. Donation
* Display in sortable and paginated table

This is not well optimized. Each user stats are grabbed individually
via the stats and transaction classes. It would probably make sense to
expand the statistics class to list a full user list with all statistics
available instead to cover this in a single SQL query.