Put Options for the Dropdown in their own type

[jachin]

I've been seeing a lot of issues with the dropdown. An example would be #141.

I think this will be easier to work on if we can make some types for the options that should go in the drop down. The idea is that once we figure out what options should be in the dropdown we wrap that in a custom type.

This should allow some more encapsulation of some of the view logic too.

I also think there's some logic that's being repeated (for instance filtering out the selected options) that we might be able to remove.

Another way of putting this, we have a lot of functions that just operate on lists of options. If we can be more explicit about what these options are going to be used for it should make things more clear.