Fix Python Recipe

A few key changes:
 - Use only the external libs in `recipe/external`. No need to have it duplicated in `recipeGIT`
   - This should fix the checkout error when running `clone --recursive ...`
 - Fixed the link used for downloading HDF5. Old one was deprecated.
 - Removed `environment.sh` and  `install_python.sh`, and replaced them with symlinks to the original versions in `recipe`. No need to keep track of duplicated, identical files.