Implemented collapsible panels for each input

- Panels contain a "wrench" icon for de/collapsing, and a trash icon for
  removal.
- validators still to be treated.
Styled contents of each input

- validators are in panels
  - validator options are list-group items
- use trash icon everywhere
- Put secondary input for options side-by-side
  - put add/cancel buttons beneath inputs
Merge branch 'hotfix/inputfilter-pane-styles'

Better cosmetics for the input filter tab