GUI: implemented scrollable suggestion list for filter widget

- Implemented scrollable list of suggestions for filter widget.
  - They now do not overflow from browser window (max. 300px height).
  - Navigation by keyboard is kept and scroll position follows selected items.
  - Automatic padding change if scrollbar visible to ensure items are not hidden.
- Change is made by using modified sources of original widget located in
  original package. This will ensure using our implementation instead of native
  and prevent need to implement a lot of other classes which work with SuggestBox.
Merge pull request #254 from zlamalp/suggest

GUI: implemented scrollable suggestion list for filter widget