Testing with julia

[lmiq]

This PR adds a new testing framework, which computes the minimum distance of the output file generated by packmol using the CellListMap.jl Julia package.

This will allow us testing the implementation of PBCs in different contexts, as CellListMap.jl supports them.

To add additional tests, include the appropriate input files in testing/input_files and testing/structure_files and add the corresponding line to test.sh, which currently is:

julia runtests.jl ./input_files/water_box.inp \
                  ./input_files/ieee_signaling.inp \
                  ./input_files/mixture.inp \
                  ./input_files/spherical.inp \
                  ./input_files/bilayer.inp \
                  ./input_files/solvprotein.inp