SpaceGroup class and new Dialog

The SpaceGroups class is formally independent of Spglib but uses it's
struct to store cyrstal system, bravais lattic, symbol and other
information. The unitcell class now only stores the Hall index
and futher look-up is performed in SpaceGroups

The spacegroupdialog box sets it values from SpaceGroups and will
be used to query and assign the space group of the molecule.

I need to shrink the width of the columns.

Change-Id: Ife5be28233aea4c4b2f26e740d595e63b273c4f0
added space group setting

At least the look is nearly completed. Some space groups have only
one setting, but otherwise I would need to make sure that the first
setting is automatically clicked. The harder part might be that I'm
not sure how indexing actually works in the QStandardItemModel so that
I can tell exactly which hall number I've selected.

Even harder still is getting the preview column to disappear and draw
details of the space group in the QGraphicsView. I might need at least
three new classes to accomplish this task.

Change-Id: I8e98d1f7a78bef04c7ff1b83ddc31151e2a1a21e