Effects > Lens flare: integrate into main project

Many thanks to @audioglider for another brilliant tool!

(Also in this commit, I have removed some unnecessary PNG files from the
repository.  Experimental menu items shouldn't have icons, to make it
easier to shuffle that menu around as needed.)
New Effects > Transform menu

In my ongoing attempts to bring order to the madness that is PD's
Effects menu, I've created a new Transform menu.  The more "serious"
and/or menial distort functions (pan and zoom, rotate, shear, etc) have
been moved to this menu, while the fun and/or silly distort operations
remain in the Distort menu.  I think this provides a reasonably clear
separation, while also trimming down the Distort menu to a more
reasonable size.