Update Save Search modal

Closes #626 

Updates to improve user experience when saving a search:

- Make Save come after title field in tab order
- Change Cancel button to a button link
- Make title a required field
- Put focus on title field when modal is displayed

![default_exhibit_-_blacklight_search_results](https://cloud.githubusercontent.com/assets/101482/2681932/76bae086-c193-11e3-8872-bf83ed2b654c.png)