Remove a prefix from a method name by manually resolving methods
Add a lifetime parameter to the ElementHelper trait

This refines the lifetime used in get_local_name / get_namespace and
makes it independent of the lifetime on the &self parameter.
Disambiguate methods without using trait objects
Refine a lifetime parameter on TElement's get_local_name
Convert the remaining ElementHelpers methods to take self
Add Copy bounds to TNode / TElement
Convert TNode / TElement to use self methods rather than &self
Remove an unused lifetime parameter
auto merge of #3540 : zwarich/servo/more-jsref, r=jdm