convenience methods for other tx-types

[marc0olo]

I think at least for PayingFor and Spend we should introduce this

• PayingFor
• Spend
• NamePreclaim
• NameClaim
• NameUpdate
• NameTransfer
• NameRevoke
• OracleRegister
• OracleExtend
• OracleQuery
• OracleRespond

[marc0olo]

question is how to deal with optional txOptions. as we introduced ContractTxOptions I think we should introduce a base-class with all common attributes