Bug 1035062 - (Part I) Remove unused isContinousSpacePressed

remove unused variable
Bug 1035062 - (Part II) Move double tap monitoring to ActiveTargetsManager
Bug 1035062 - (Part III) Remove resetUpperCase()
Bug 1035062 - (Part IV) Make setUpperCase take a state object
Bug 1035062 - (Part V) Use state object in IMERender.setUpperCaseLock()
Bug 1035062 - (Part VI) Remove the NO_OP special keyCode
Bug 1035062 - (Part VII) Remove resetScroll from IMERender.toggleCandidatePanel()
Bug 1035062 - (Part VIII) Implement CandidatePanelManager
Bug 1035062 - (Part IX) Implement TargetHandlersManager
Merge pull request #21898 from timdream/keyboard-target-handler

Bug 1035062 - Implement TargetHandlersManager, r=rudyl