Add configurable quorum caps to the economic protocol
Minimum and maximum quorum caps are added to the constants of the economic protocol. Whenever a voting period would cause the quorum to go below or above the caps it will be bound to the limit defined in the constants.
In the future token holders can easily modify the caps by changing the constants.
This commit amends the context of athens_004 and adds min/max quorum caps to it. Initially the minimum quorum cap is set to 30% and the maximum to 70%.