Model: more scalaesque factory methods

In order to interact better with the json combinator lib
the factory functions now take Option and Seq instead of null
and util.Set.

Test adjusted.
made an example split of the response for HTML/JSON
draft implementation of the JSON parser for conferences
draft implementation of the Serializer using built-in Format, Reads and Writes
removed prototypes from the Conference controller
Serializer - moved buildObj to the class scope. deprecated separate Reads inside the class
made a package object from the Serializer
changed URL composition in Serializers
made some Serializer fields nullable
fixed small issues with naming, imports
fixed model changes
fixed model changes
refactor Serializer, removed intermediate object builders
two diff branches merged