Sorting and grouping are incorrect

[zepheiryan]

As discovered in #55, there is a bug surrounding sorting and grouping. Taking the Nobelists demo as a sample, multiple sorts will start to show some sub-groups as children of their sibling order instead of siblings, and some sub-groups will simply be missing. The algorithm for generating these does not appear to be entirely correct.

Note that the changes that temporarily fixed #55 should be backed out once this is repaired; they will be unnecessary.

[zepheiryan]

This change is too aggressive given the default on ordered views is to use grouping. Anybody sorting by label is going to get something of a surprise with this change. Backing out d3e1f08 and going back to the fix used in #55 for now. A better solution probably involves using a hybrid, keeping things as they are when only one level of sorting is used, breaking out one item as a group behavior when more than one level of sorting is used.