OTNumList: rename class to NumList
OTNumList: rename files to NumList.{h,c}pp
Merge pull request #471 from toxeus/renameOTNumList

OTNumList: rename to NumList
Rename getTransactionNumber functions to match the getTransactionNumbers message.
getTransactionNumbersResponse: allocate a separate transaction
number for the receipt instead of reusing one of the numbers signed out
to the client.