Hive Engine - Increase Number of Witness Positions

This update includes the following:

• Number of top witnesses increased from 6 to 10. One additional witness will remain in the backup position (so total changed to 10+1 instead of 6+1).
• Number of witness signatures required on new blocks increased from 5 to 9.
• Max round proposition waiting period decreased from 40 blocks to 20 blocks and changed to be based on sidechain blocks instead of Hive blocks.

PRs included: #44

Note that no change to the behavior of the node software will occur until the corresponding witnesses contract upgrade is deployed. All witnesses and other node operators are required to upgrade before the deployment of the witness contract upgrade.