implement xml event attributes for actions

[JoernT]

implement following attributes according to xml events spec:

• [x] event (done)
• [ ] observer
• [x] target (done)
• [ ] handler
• [x] phase
• [x] propagate
• [x] defaultAction

[JoernT]

goes to 'minor' now as 'observer' and 'handler' are considered rather rare use cases for now.