Batch methods gas optimization

[zajck]

Description:

As already pointed out in #511, expireDisputeBatch calls expireDispute in every loop iteration, therefore it checks if dispute region is paused every time. There are also other examples of the same issue:

• extendOfferBatch
• voidOfferBatch
• completeExchangeBatch

Fixing this requires a bit of refactoring and perhaps a different approach to how internal functions work in this cases.