Bug 1015643 - (Part I) Implement LayoutLoader for loading layouts
Bug 1015643 - (Part II) Implement LayoutManager
Bug 1015643 - (Part III) Include layout_manager.js in keyboard.js
Bug 1015643 - (Part IV) Use LayoutLoader in keyboard.js
Bug 1015643 - (Part V) Use LayoutManager
Bug 1015643 - (Part IV) Unify layout activation to updateCurrentLayout()
Bug 1015643 - (Part V) Width = 3 for number layouts
Merge pull request #19811 from timdream/keyboard-layout-state

 Bug 1015643 - Unify layout activation to updateCurrentLayout() and use LayoutManger & Loader, r=rudyl