[Events] uiactions IDL attribute is now a DOMTokenList not a DOMString

The uiactions IDL attribute is now a DOMTokenList not a DOMString,
The uiactions content attribute is still a string, of course.

For those of you unfamiliar with DOMTokenList, this means Element.uiactions now behaves like Element.classList, where before it was set up to behave like Element.className. This change makes it easier for authors because they won't have to do string parsing on the property or add libraries to handle adding, toggling, or removing actions.
> 2.1 The uiactions IDL Attribute
> 
> The uiactions attribute of each instance of the Element interface must return a DOMTokenList reflecting the uiactions content attribute.
> 
> partial interface Element {
>     readonly    attribute DOMTokenList uiactions;
> };
> 2.1.1 Attributes
> 
> uiactions of type DOMTokenList, readonly
> A DOM element attribute whose DOMTokenList value reflects the value of the uiactions content attribute.
> This attribute is readonly b/c DOMTokenList values are modified by methods (e.g. el.uiactions.add("pan");) rather than by string assignment (e.g. NOT el.uiactions = "pan";). Need to make sure this is clear for authors.
> 


Link
https://dvcs.w3.org/hg/IndieUI/raw-file/default/src/indie-ui-events.html#uiactions-attribute

Changesets
https://dvcs.w3.org/hg/IndieUI/rev/3ab9f0b62e4d
https://dvcs.w3.org/hg/IndieUI/rev/ca0e9a3513d6