rethink element endpoints and grouping strategy

[CaptainN]

To make the nested naming stuff easier to deal with, it might make sense to think about the bottom level elements differently when it comes to select boxes, and add a grouping mechanism for any elements that use the square bracket syntax. Currently, I've got the field extractor looking for selects first, then looping options, rather than looking for the bottom element - the options, then grouping them appropriately through a more generic grouping mechanism, which could apply to any grouped elements (using the php square bracket syntax). Selects would just be a version of grouping that works on DOM parenting instead of name based grouping.

Thinking about grouping this way fits the constraints of the request data (and therefor our DOM query options) better.