modified way to provide microstructure input in json

[sanathkeshav]

Solves #40 and #41.

Previously:

"ms_filename": "microstructures/sphere32.h5",
"ms_datasetname": "/sphere/32x32x32/ms",
"ms_L": [1.0, 1.0, 1.0],

Now:

"microstructure": {
        "filepath": "microstructures/sphere32.h5",
        "datasetname": "/sphere/32x32x32/ms",
        "L": [1.0, 1.0, 1.0]
 },

Previously, results would be written to h5 file in the group /datasetname/...., now it will be written to /datasetname_results/....

[claudiushaag]

LGTM!