New CV, View, Show, Control Points option to always be able to see BCP

As an added bonus, when this mode is on, you can also grab any BCP and
move it without having to select the splinepoint what owns the BCP you
want to move. That is: you can just grab any visible BCP and move it
as you like.
Merge pull request #684 from monkeyiq/2013aug/alwaysshowbcp

New CV, View, Show, Control Points option to always be able to see BCP