Changing upstream share finding function

* 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!
Merge pull request #82 from TheSerapher/upstream-share-by-order

Changing upstream share finding function