Implement filtration on backend side

* add possibility to filter, sort and limit data(see [here](http://developer.myob.com/api/accountright/api-overview/retrieving-data))
* add convenient `find` method to find by `UID`
* cleanup code(always use old style hash syntax for consistency, remove `{}` when hash passed as last arg)
@davidlumley Just updated this line, because it weren't working as expected.