The pooled fees in the parent universe should be migrated to the winning universe

[CrystalBallBe]

Is your feature request related to a problem? Please describe.
The problem is that settlement fees are pooled in the parent universe even after a fork end. This causes two issues.

1. Settlement fees that are pooled in the parent universe will be stacked.
   If all REP in the parent universe are migrated to child universes during a fork, settlement fees that are pooled in the parent universe will be stacked. Since no one can purchase participation tokens in the parent universe after a fork ends.

2. REP in the parent universe will not lose their value.
   In order to further the migration, REP in the parent universe should be completely worthless after a fork ends. But if huge fees should be expected to be pooled in the parent universe after a fork, it will be less motivated to migrate REP. Since REP holders can receive those fees by purchasing participation tokens in the parent universe. That makes the REP valuable in the parent universe.

Describe the solution you'd like
After finalizing the forking market, settlement fees that are paid in the parent universe should be pooled in the winning universe,

Additional context
In the current system, dispute windows in the parent universe are not migrated to any child universe, they are created anew. (I looked into the contracts with my untrained eye, so I might be wrong)

• Regarding the winning universe, dispute window is created when the non-forking market is first migrated to the winning universe.
  

  augur/packages/augur-core/src/contracts/reporting/Market.sol

  Line 426 in 959cabf

  disputeWindow = _destinationUniverse.getOrCreateNextDisputeWindow(false);

• Regarding losing universes, dispute window is created when the initial reporting is first done in the losing universe.
  

  augur/packages/augur-core/src/contracts/reporting/Market.sol

  Line 126 in 959cabf

  disputeWindow = universe.getOrCreateNextDisputeWindow(true);

Reference: msagansk/Augur.Guide#60

[CrystalBallBe]

2. REP in the parent universe will not lose their value.

I take back my words about that👆. Since after a fork starts, users cannot purchase participation tokens in the parent universe due to this line in the contract.