Add json serializer and deserializer

...in/java/de/tobias/playpad/server/json/JsonCollection.java

src/main/java/de/tobias/playpad/server/json/JsonName.java

src/main/java/de/tobias/playpad/server/json/JsonObj.java

src/main/java/de/tobias/playpad/server/json/JsonParent.java

.../scala/de/tobias/playpad/server/json/JsonSerializer.scala

.../tobias/playpad/server/json/NumberSerializerHandler.scala

...ala/de/tobias/playpad/server/json/SerializerHandler.scala

.../tobias/playpad/server/json/StringSerializerHandler.scala

...de/tobias/playpad/server/json/UUIDSerializerHandler.scala

src/main/scala/de/tobias/playpad/server/project/Design.scala

src/main/scala/de/tobias/playpad/server/project/Pad.scala

src/main/scala/de/tobias/playpad/server/project/Page.scala

src/main/scala/de/tobias/playpad/server/project/Path.scala

...main/scala/de/tobias/playpad/server/project/Project.scala

...a/de/tobias/playpad/server/project/ProjectReference.scala

...ias/playpad/server/project/loader/json/DesignLoader.scala

...tobias/playpad/server/project/loader/json/PadLoader.scala

...obias/playpad/server/project/loader/json/PageLoader.scala

...obias/playpad/server/project/loader/json/PathLoader.scala

...as/playpad/server/project/loader/json/ProjectLoader.scala