Add DocumentAndElementEventHandlers - #413

Do I need to make something like:

<attributecategory
      name='document and element event'

that lists all event handler attributes in DocumentAndElementEventHandlers and add them to all 44 places in SVG? This seems to defy the point in mixins if we have to maintain every content attribute that reflects a IDL attribute in a mixin that is defined in another spec.

Do I need to make something ... that lists all event handler attributes

Good point. Technically, the mixin only defines the DOM interface properties. It doesn't add the attributes to the element model. So the attributes do need to be defined separately.

That said, the text in the Event Handlers section in the interactivity chapter is pretty open-ended, automatically including any new event types:

event attribute
An event attribute always has a name that starts with "on" followed by the name of the event for which it is intended. It specifies some script to run when the event of the given type is dispatched to the element on which the attribute is specified.

For every event type that the user agent supports, SVG supports that as an event attribute, following the same requirements as for event handler content attributes [HTML]. The event attributes are available on all SVG elements.

So maybe a better strategy would be to get rid of the list of explicit attributes for the "global event attributes" category, and instead make it link to that section. But I'm not sure where in the build process we need to change something to make that happen.

Until we work out the build process, I'll just add DocumentAndElementEventHandlers every where that GlobalEventHandlers is included for now. As it is for cut/copy/paste it probably won't change too much, unless onbeforecut/copy/paste are standardized (which are supported by all browsers)

@dirkschulze / @AmeliaBR : this should be ready for final review I believe.