Fixes AWS query maps inc. SNS mobile push features

These changes should fix the SNS mobile push operations that include the `Attributes` parameter (see #136). It updates the `AwsQueryVisitor` class to support customizable map key and value names, but defaults to what the AWS query protocol expects if none are specified, as is the case with the SNS operations affected by the issue. This fix also updates the SQS and CloudSearch services description in addition to SNS, because they are also affected by this change.