make gnt.h a single include file

Move the ncurses bits to a new gntncurses.h.in setup

Move all the function prototypes from gnt.h to gntmain.h since thats where they should be

Move the KEY_EVENT undef to gntncurses.h as that's where it is needed

create a global header file and don't let the library use it

Add the single include header guards and deal with fall out

Testing Done:
Compile testing and ran all of the manual tests.

Reviewed at https://reviews.imfreedom.org/r/62/