Fix for #39 (Nil union values not handled properly by jackson)

[Kaiser1989]

Here is my Pull request for Ticket #39

Following things changed:

• Changed complete behaviour of Jackson-Deserialization
  • Don't use deserialize to Map anymore, use JsonNode instead
  • Added deserialization strategy for every TypeDeclaration
  • Unions, Arrays and Any Types are not supported
  • Sorting of types for better deserialization (integer before number)
• All Unions are working fine:
  • Objects, nil and primitive types
  • Inline declaration and type declaration
• Throwing an Ambiguous Exception if ambiguous types are used
  • This needs to be done as two String types cannot be distinguished when in Json Format anymore
• Changed ObjectCreation for Unions to create correct inline types
• Changed structure of Unions:
  • Changed union name (string | integer | nil => StringIntegerNilUnion)
  • Instead of one "any-field" all types have their own field (anyfield was removed)
  • This is needed, as validation cannot be done on a single field (imagine a Email (string with pattern) and nil union)
  • Created enum of types in unions to allow Switch statements, not asking every field
• Added field creation to JSR303 to add validation for union fields
• Changed naming of union fields to match the given type (Email (type String)) is now used as Email and not as String anymore (isEmail, getEmail)
• Moved implementation from jackson2 to jackson (without jackson2 stuff)
• Added jackson2 test
• Added validation test
• Fixed some formatting in SpecMatchers