Rename Transfer.options foreign key to option
Fix if statements that treated a dollar amount as boolean
Fix overly verbose Transfer creation statements
Rename LineItemChoies.options_str to option_choices and add docstring
Rename 'cost' field in MultiSelectCostItem to 'option' for clarity
Fix a lingering reference to LineItemType.options_str
Switch from using an ID (or None) to an object (or None) in create()

I guess there was a reason for having that extra code before, it was
just a bit too verbose.  I think this is the most concise approach
that works.
Make option choices show up in Transfer admin list