PayoutContract: Fixing payout distribution, and tests

[villesundell]

Problem involving payouts is now fixed, using @voith's math. Now payout tokens can be more or less numerous than the available security tokens.

Also, tests are improved to check that payouts are being paid correctly. Both scenarios (where payout tokens are more or less numerous) are tested.

[villesundell]

The master was recently updated introducing a conflict, I will solve :)