modules: updated FindCorrade.cmake and FindMagnum.cmake.
Updated toolchains submodule.
Advertise NaCl, Emscripten and Android ports in README.
viewer: pass reference instead of pointer.
viewer: use MeshTools::compile().

Makes the stuff simpler.
modules: updated FindMagnum.cmake from Magnum repository.
doc: fixed reference.
modules: updated FindCorrade, FindMagnum and FindMagnumIntegration modules.
Merge branch 'master' into compatibility