Fixes discouraged static table object and SlickDDLPlugin when referring to vals in AutoDDL

* Replace static singleton table objects with vale. From the Slick docs "Also make sure that an actual object for a table is not defined in a static location (i.e. at the top level or nested only inside other objects) because this can cause problems in certain situations due to an overeager optimization performed by scalac. Using a val for your table (with an anonymous structural type or a separate class definition) is fine everywhere." http://slick.typesafe.com/doc/1.0.1/lifted-embedding.html#tables
* SlickDDLPlugin now handles LinkageError, which can happen, when referring to vals in AutoDDL, because it is loaded via reflection.