Faking mouse clicks is a stupid way to do it of course. Try to do it
"right". For now just worked on moving the end handle, but once that
works, similar code should be used for the start handle, too.

Does not work yet. It is hard to extract out from
SwEditWin::MouseButtonDown() exactly what all is relevant, and what
isn't, for this use case.

Change-Id: I76a226f787facbac645aaff8b4852d693bcf4ccb