Increase the maximum TM due to the introduction of the subnodes

#### What would you like to be added:
Increase the TM from 57 to a bigger Number

#### Why is this needed:
with the integration of the subnodes and the increasing amount of masternodes there is already a huge amount of subnodes at TM 57 no matter if they found 2 or 3 weeks ago the last block.
Perhaps it would make sense to extend the 14 days to 28 days in order to maintain equal opportunities.
Attached a graph over the targetmultipliers, Somewhat affected by the many frozen nodes at Cake in the front TM areas.