Rotamer dialog column sorting not numerical

[Elaine Meng]

If I calculate clashes for Arg rotamers at 3gws residue 346 (Leu) and then sort on the clashes column, it thinks 8 is larger than 38, for example (image attached). It may never be seen for the hbonds since one rotamer is unlikely to make >9 hbonds.

[pett]

Need to get underlying table widget to support numeric sorting by subclassing QSortProxyModel and overriding lessThan(). Also need to add support to _ItemColumn (explicit 'numeric' attr and/or custom sort func)

[pett]

For now, just assume that items that look like numbers are numbers and sort accordingly. Add explicit control over case and numeric sorting later if actually needed.