Add QuantumEspresso_jll.jl as pw.x executable

[singularitti]

Just setting the path to the executable may not let pw.x usable since we still need to export library path, etc. If this is not carefully done, pw will not execute:

julia> pw("p=10.0/SelfConsistentField.in", "p=10.0/SelfConsistentField.out")

So I may consider using QuantumEspresso_jll as the source of pw.x though it has some trouble.

$ /home/parallels/.julia/artifacts/c3375c4006f7ee5e2507aea85778849335e60521/bin/pw.x < p=10.0/SelfConsistentField.in > p=10.0/SelfConsistentField.out
/home/parallels/.julia/artifacts/c3375c4006f7ee5e2507aea85778849335e60521/bin/pw.x: error while loading shared libraries: libxcf03.so.9: cannot open shared object file: No such file or directory

[singularitti]

This was implemented and removed in #56.