rename my-app to app round 2

[3cp]

As discussed before, <app> does not work if user chooses ShadowDOM setup (the spec requires at least a dash in tag name).

[brandonseydel]

@3cp - Shadows dont require a - but it requires it of a non standard tag....maybe a div with app....or just make it something more production ready other than my-app or just leave it app as that is 99% of users first sequence of events