Fix broken debouncing on search control textbox

Fix #502.

The issue was that the triggerSearch event wasn't debounced until after the call to the super constructor. This meant that the event was already bound to the non-debounced version of triggerSearch before triggerSearch became debounced. I changed the ordering and added a new _triggerSearch method for clarity.

Signed-off-by: Don Naegely <naegelyd@gmail.com>