Trade::MeshData const-correctness.
Trade::MeshData const-correctness.

"Counting" functions are always constant, added const versions of data
accessing functions, so MeshData can be now passed and used as const
reference.

MiUishadow/magnum,ashimidashajia/magnum,DerThorsten/magnum,MiUishadow/magnum,MiUishadow/magnum,ashimidashajia/magnum,DerThorsten/magnum,MiUishadow/magnum,ashimidashajia/magnum,DerThorsten/magnum,ashimidashajia/magnum,DerThorsten/magnum,DerThorsten/magnum,ashimidashajia/magnum,MiUishadow/magnum,MiUishadow/magnum