Deferred Fog Opacity/density controls.

[CarbAndrewD]

Deferred Fog Opacity/density controls.

[akioCL]

Fog Opacity is controlled using the start and end distance. The greater the distance between them, the less opacity the fog has (but it always is 100% at the end distance).
Since the problem seems to be the max density for the fog (since it's blocking the Skybox) I added a "Fog Density Clamp" attribute that limits the max value for the fog opacity. I also added 2 new modes for the fog formula, Exponential and Exponential Squared, with a density value that controls the way the density ramps up.
Finally the Fog Layer functionality was enabled for the Mobile pipeline. It's a little more expensive than the traditional deferred fog, but Shader Variants were added when the Fog Layer is on/off. Also, Fog Layer (and Turbulence) are disabled for low and medium mobile devices.