* Added: API String QR Code for #582 and #591
This will allow more QRCodes being added that are specific to an
account. The require library is added and the API string can be used as
an example how codes are generated.
Fixes#582
* 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.