Major revision to Acceptable and Not Found logic

- remove Accept param from constructor, convert to setAccept() method

- rename notFound() to isFound(), reverse the return values, and move from AbstractBlogResponder to AbstractResponder

- rename notAcceptable() to isAcceptable(), reverse the return values

- rename responseView() to renderView()

- in Actions, do not pass $acceptable to Responder, call setAccept() instead

- change the boolean logic in Responder __invoke() methods to something more readable
reorder methods