WadMapConverter|Id1Map: Use the LumpIndex API to locate map data lumps

Rather than have the Id1Map converter negotiate the old and obsolete
WAD API, provide the converter with the LumpIndex to use when locating
map data lumps.

As a LumpIndex is used both at WAD file level and globally for central
lump index, this means one can now convert a specific map independent
of DOOM's old fashioned global lump index mechanism.