Made the select pageable

[olafgeibig]

Sorry, I don't know scala so I coded like java. I made just a small change to optionally make the select statement able to page with LIMIT and OFFSET. This was trivial as MySQL and PostgreSQL share the same syntax.

[Narigo]

This would be perfect if you could add some tests :)
And maybe you need to sign the eclipse CLA, since this is an "official" vert-x module. Not sure how I could see that... 😕

[Narigo]

@olafgeibig while porting the module as a service to Vert.x 3, I've seen that MySQL and PostgreSQL are not completely the same in that regard. In MySQL you always have to provide a LIMIT clause, but in PostgreSQL you don't. So my workaround there was this: https://github.com/vert-x3/vertx-mysql-postgresql-service/blob/initial-work/src/main/scala/io/vertx/ext/asyncsql/mysql/impl/MysqlOverrides.scala#L16