Add icon to make edit in place affordance more clear

Fixes #572 

Adds an edit icon when the user hovers over the display label area for these Curation pages:

- Search facets
- Feature pages
- About pages

As part of this, adjusted things so the user can click a broader area than just the label itself to trigger the display of the input field for editing.

Example where mouse is hovering on the left side of the Personal Names facet panel:

![curation_-_search_facets___default_exhibit_-_blacklight](https://cloud.githubusercontent.com/assets/101482/2609937/d70b9b5e-bb7d-11e3-8a27-ad65292e138f.png)