ENH: Fix help button alignment in Builder dialogs

In Builder's properties dialogs the alignment of the help buttons did
not match the okay and cancel buttons. The cause for this was that the
flags for Sizer's Add() method were passed to the wrong parameter. This
was fixed by adding the missing passing of 0 for the skipped parameter.
Merge pull request #406 from philippwiesemann/master

ENH: Fix help button alignment in Builder dialogs