Bug 995128 - Suggestion list should use the building block action menu

- Move the suggestion-item to an HTML import
- Prefix all classes used for JS DOM selection
- Remove the transition when the overlay opens since it was not visible on device
- Reorganise the test file to separate SuggestionBar and SuggestionList tests
- Add some new tests
- Move suggestion bar related styles out of keypad.css
- Used the BEM syntax for classes