add RequestHandler and ModelController fixed #32
todo_controller.js: change action-attribute in parameters-array for ajax-request
Modelcontroller.php: delete unused variable, change __construct() and rename function
RequestHandler.php: relocate return statement
Tickets.php: rename function
#issue in comment
Merge pull request #34 from Canbanizers/create_RequestHandler_#32

create request handler and modelcontroller, add some testcode to show implementation #32