edit forest change text on data page


![section to be styled](https://f.cloud.github.com/assets/5981931/1891685/b613c066-7a41-11e3-9534-e363b0915c3e.png)
Edited forest change text on data sources page, including general description of forest change layers, titles of some layers, and FORMA text. 

NOTE: the text under the "Accuracy and validation" section of FORMA needs to be styled (the list should be indented) - SEE ATTACHED