#2 menu option to swap left/right mouse buttons

[Jonathan Cheyer]

The "official" mappings (according to documents we have
seen) for the left and right mouse buttons (with no
keyset key pressed) are:

left (100) - <BC> (backspace)
right (001) - <OK> (return)

This mapping is used by the DOS AugTerm.

The Visual AugTerm (VAT) seems to have the default
mappings swapped (right is backspace, and left is return).

The Java AugTerm should use the official mappings by
default, but it should allow the user to swap the
mappings so that it can also work like the VAT.

Add a menu option to do this, and also add a command
line option.