Builder character count view refinements (#562).

- Remove unnecessary _.defaults call.
- Upgrade to jquery.tooltipster 2.1.4.
- Use a tooltip rather than inline text to display warning about
  over-character-limit inputs.
- Stop polling when sections change--don't wait for a blur event.
- Add a warning-color set to variables.less.
- Use warning colors and icon to highlight over-limit character
  counts.
- Prevent input elements from moving in summary section when
  character count is revealed.