Show disabled options

@kenearley @stof 

This takes @kenearley's #1177 and runs crazy with it. The big changes:

- Shows all options that match a search (whether or not they've been disabled or selected)
- Disabled options get a grayed out style
- Selected options in multiple Chosen get a grayed out style
- Removes the expensive ``winnow_results_clear`` method
- Cleans up the ``results_highlight`` method

This is a pretty big change in functionality and code. I'd appreciate a fair amount of click testing before your +1. I've been trying to make bugs, but haven't found any yet. I bet they exist.