Add spack package for WABBIT

[freifrauvonbleifrei]

I tried installing WABBIT on my laptop and ended up creating a spack package, which may be useful for portable installation ;)

here's a minimal example of how one can use spack to install WABBIT with the package files in spack_repo

git clone git@github.com:spack/spack.git spack-v1.0.2

# set up spack environment -- adjust first path as needed
# this avoids using the home directory for spack config and caches
export SPACK_PATH=$(pwd)/spack-v1.0.2 && export SPACK_USER_CONFIG_PATH="${SPACK_PATH}/user_config" && export SPACK_SYSTEM_CONFIG_PATH="${SPACK_PATH}/sys_config" && export SPACK_USER_CACHE_PATH="${SPACK_PATH}/user_cache" && . ${SPACK_PATH}/share/spack/setup-env.sh

cd spack-v1.0.2/
git checkout v1.0.2

# ...load all the usual modules ...
spack compiler find
spack external find

spack repo add ${WABBIT_ROOT}/spack_repo/wabbit
spack spec wabbit

# either install the default version (currently 1.0-CiCP21 )
spack install wabbit

# or go to the folder where the wabbit git repository is cloned and build there:
spack dev-build wabbit
# -> will put the build folder into this directory, and if installation succeeds, it will be installed into the spack store too
# (needs to be removed, with spack uninstall, and reinstalled when the source code changes)

you can test it and consider contributing it to spack-packages, or just keep it here in the repo.