FF: Fix NameError when using keyboard component

After recent changes it was not possible to use the keyboard component
because opening the property dialog raised a NameError. This was fixed
by using an available Sizer.
ENH: Corrected comment in builder source
ENH: Comment debug print in builder source
Merge pull request #459 from philippwiesemann/fix-builder-keyboard-crash

FF: Fix NameError when using keyboard component