Reorganized the environments page to flow better.

- Added details about how to set the environment for an application
- Added details about setting the environment for Oil
- I updated the information regarding server environment variables as stevewest suggested. Let me know if this is still inaccurate. 

Signed-off-by: Zechariah Campbell
The green lines are things you have added or changed, then the red are things that have been removed.
"There are two ways to set your environment in FuelPHP. The third option below shows you how to set..." could be a little confusing, "If there are only two ways then where has the 3rd suddenly come from?"