Add BEAN and BPLUS targets for optiboot.

[mjbrown]

Add build targets for bean and bean+.

[swstack]

@mjbrown make sure you assign someone (on the right hand side of window).

[swstack]

Also, I assume that the actual content for this change did not require 1,133 additions and 6,301 deletions...so i'd recommend splitting out your changes in multiple commits, one of which I assume was a formatting change or the removal of dead code?

[mjbrown]

The resulting .hex files are checked in so that people don't have to do a substantial amount of environment setup to build the image. I am following how it was done before because the drawbacks of this approach are insufficient to justify a change.