2.1 and SetHandler

[ZOS_ChipHilseberg]

We've been profiling some UI code since 2.1 went live and we've noticed some spikes with SetHandler on controls. Especially when the code is frequently making a new anonymous closure and passing that to SetHandler. In a lot of cases this can be avoided during play time by setting the handler on the control in the XML or on a template (virtual = true) in the XML so that cost is paid during the load. The handler closure should also only be made once instead of every time SetHandler is called, by storing the closure in a local or on a table.