Adding ```deviceType``` criteria filter

For [AGPUSH-41](https://issues.jboss.org/browse/AGPUSH-41) the "selective sender" endpoint gets a new  ```deviceType``` criteria filter.

For that some changes to the DAO and the sender service have been applied:
* getting rid of java iterations for "fetching" the device instances
* Introduced a generic/dynamic JPQL to just fetch a list of device tokens (that's all we really need for sending)
* Overhaul of the actual endpoint: Using classes, instead of maps. 
* Passing "meaningful maps" to the sender service