Fix the clunky select/input element numbering.

Make use of the bootstrap input-group and input-group-addon.
The change including:

- Replace <li> and <ol> with <div>.
- Gives a ".form-horizontal" and ".form-group" class
  to respective element.
- Surround `SeriesSelect` with an '.input-group' class
- Add `inputAddon` variable/props, the element that represent the index.
- Update `categoryForm` logic in Votes.js