ISIS-651: minor improvements to core

... to better support JRebel (in testing Estatio).
ISIS-486: double checking URL return value...

... for actions that take params.

Have done this by minor refactor to the ToDo app.
ISIS-651: adding a .launch for todo app also.

In addition:
- delete the rebel.xml files checked in for simple app
- update .gitignore to ignore rebel.xml files.
- minor tidy up of ToDoItem
ISIS-656: fixing role memento for shiro