Highlight support for generalized line specials

- Boom's generalized line effects now highlight affected sectors and
affecting linedefs as expected. This is done by having a dummy action
special stored in the game configuration class that is returned when the
special type is within the range occupied by Boom's generalized specials
and Boom extensions are used.
Distinguish between manual and switched genlines

Duplicate the dummy Boom generalized specials. One of them is for
"switched" specials (affect tagged sector), the other is for "pushed" or
"manual" specials (affect back sector).
Merge pull request #11 from Gaerzi/master

Highlight support for Boom's generalized line types