Builder title gets a character count view (#562).

In builder:

- Take baked-in character count behavior out of RichTextEditorMixin.
- Make CharacterCountView, a reusable view that tracks character
  counts in inputs and wysihtml5 editors.
- Rename RichTextEditorMixin.getEditor to createEditor. Add a
  getEditor method that just returns the created editor.
- Update default warning text of character count view to
  "Shorter is better!"
- Give the summary section title a character count, with a limit of
  100 characters.
- Update copy in placeholder of summary title text.
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.
Remove bold weight in builder summary title (#562).
Remove old version (1.2) of tooltipster (#562).
Merge pull request #839 from patternleaf/562-story-title-char-count

Merge implementation for issue #562: Story builder should issue a notification for long titles