Refactor|libhexen: Switched in_lude.c to C++
Refactor|libcommon|libdoom|libheretic|libhexen|libdoom64: Use de::LumpIndex's C++ API
API: Dropped old/obsolete W API

The specialized lump index functionality of this old API can now be
accessed directly via de::LumpIndex's public API. The central lump
index can be accessed via the F API's F_LumpIndex().

libcommon provides a convenient CentralLumpIndex() accessor function.