#JC-1144: Implemented custom handler mapping.
*Now each plugin can define own controller class annotated with @Controller annotation and declare in this class method annotated with  @Request mapping annotation which will handle requests.
*Implemented simple QuestionsAndAnswersController which redirect to blank page by "/question"
*Web controller plugin became abstract class with handler mapping implementation
 *NEXT STEP: figure out how unmap request handler when plugin disabled/removed