When finding more than a single block between runs it added shares to a
new block from a previous one. Properly fetch the last highest share ID
from the database prior to scanning for shares assigned to a block.
Fixes#124
To better support more payout systems I have moved the share calculation
for a block into the findblock cron. This way these statistics are
always available and not depending on the actual payout method.
* Findblocks cronjob changes
* Find & Store upstream share
* Use last found `share_id` as starting ID or `0`
* Find & Store upstream finder
* Use last found `share_id` as starting ID or `0`
* Use stored information when running propotional payout
* Fetch current checked blocks upstream share from block table
* Fetch previous upstream share of previous block from block table
* Calculated payouts in that range of IDs
* Updated `block.class.php` to store share_id in block and fetch highest `share_id`
* Fetch all blocks unaccounted for in ASC oder (low to high height)
* Use lowest height block to find lowest ID upstream accepted share
* Use this share as the finding share for a block
* Set share as last found upstream share for further blocks
* This only applies if shares are not deleted at all which they should!
