Dialog demo: Remove regular modal demo, the other modal demos are better
Dialog demo: Move animated dialog demo to the end of the index

This demo looks rather silly and has no purpose beyond showing of the
animation options. It doesn't do that very well.
Dialog demo: Update modal form demo

- Removes an invalid jquery.ui.button.js reference (button.js is loaded)
- Updates the email regex to use the one from the HTML5 spec
- Refactors the code to add the user on both button click and form submit
- Reset the form to its original state on submit
- Initialize the form with values that can be submitted immediately, better
for a demo
- Rename bValid to valid