Add option to "Hide Label"

This adds a "Hide Label" option to the PreValue Editor:
![prevalues](https://cloud.githubusercontent.com/assets/1396376/3047110/953b9bf0-e131-11e3-9c87-ff737863ef03.png)

**Example when selected:**
![notesnolabel](https://cloud.githubusercontent.com/assets/1396376/3047123/b2c4b012-e131-11e3-8f2f-3505c47493da.png)

**And not (as is currently):**
![noteslabel](https://cloud.githubusercontent.com/assets/1396376/3047144/de443a3c-e131-11e3-8ce9-7f17f0d0f410.png)