#57 better visual feedback of active component mode

[Dominique B.]

Hi,

i am still confused by the displayed vertices under
every component mode. While checking out Silo quickly i
saw that they add a little dot in the middle of each
faces, when the user is in face-mode. I think maya does
the same. For edge mode, edge could be displayed with a
different color.

I think it's important to give a direct feedback on the
model itself about the active component mode (and what
is selectable). Might add ergonomy for new users, also.