* changes reward => pricePerByte
* collateral => collateralPerByte
* updates tests
* introduces AskHelpers to compute price and collateral per slot
* adds public view function returning currentCollateral for the slot
* updates names for price and collateral
* uses pricePerSlotPerSecond in maxPriceHelper
* adds collateralPerSlot helper
* makes sure that the intended use of the <<currentCollateral>> view function is demonstrated in tests
* formatting
* fix comment
* mints more tokens so that it can be used with contracts tests in nim-codex
* Renaming <<collateral>> and <<reward>> to <<collateralPerByte>> and <<pricePerBytePerSecond>> respectively (merged in the meantime to the master)
