AsyncSQLInsertClause.executeWithKey implemented
support for AsyncSQLInsertClause added to DatabaseRef
AsyncSQLQuery improvements
handleCreateHarvestJob implemented
flatResult implemented
DatabaseRef.transactional is now generically typed

This avoids bugs where 'map' is inadvertently used instead of 'flatMap'. 

By using a more specialized (than Object) return type the compiler
raises a type error when you try to return a Future (because
Future<Object> is an Object) where none is expected.