Adjust 3 methods to reduce library requirements

The constructors for Message(JSONObject) and Message(Element) were
converted to static methods as they are only called in one place (the
servlet itself). Also refactored Message.getJSONObjects() to return the
JSONObject's parent class, HashMap<String,Object> instead. Now the JSON
library and JDOM library no longer need to be included in projects that
use the Gemini library.