Make TimeStamp in event.rs return the actual timestamp
Removed unnecessary return and moved crate import to script.rs
auto merge of #2275 : gsingh93/servo/master, r=Ms2ger

Timestamp should return the time the event was created, not 0. This fixes three test cases in dom/events/Event-constructors.html. This is my first pull request, let me know if there are any issues.