the Ja2.rc file needs to be in the add_executable target for the icon
to appear, and that one requires WinMain.
so get rid of dummy.cpp and put sgp/sgp.cpp in there
Language is now just built once per app (still some JA2UB conditionals
going on in there) but building everything should now take eight times
less work
* Move main executable files to their own directory
* Adapt the build to the new file structure
... and fix some weird #include's that were relying on the project root
being an include directory.