Widget: Improve API for direct instantiation

[Scott González]

When instantiating a widget directly (new $.ui.dialog( options, element )), the following should be improved:

• The new keyword should be optional
• When not using the new keyword, the widget should be initialized even if called with no parameters
  • When called with the new keyword, the widget should not be initialized to allow the simple inheritance pattern to continue to work
• The widget should be able to generate an element if one is not provided
• Providing a selector or jQuery object instead of a DOMElement should fully work
  • Currently the widget will be instantiated and this.element will be correct, but the instance will not be stored as data on the element

[Scott González]

Implemented in 3a0b617bb44565aacfa90c2ee20b293654d911c9 and 244eebe74dbc7bb35141e58e52ef9eaa21bd35f1.

Tests added in bc71499a505d0932668b4ae75603cd9dbfd4a2ac.

Proper default elements for all widgets in 29bfb86ce2e192dae456bf15655c25cb469ad977.