Pass on ADOBE environment variables.

[manneohrstrom]

Summary

We should do a pass on the various environment variables to ensure they are in the right place. I am seeing a lot of stuff on the engine level that looks like it likely belongs at the framework level and in some cases it is defined in both the engine and the framework, which is bad.

The goal: Get as many of the environment variables into the framework as possible. Update the documentation to reflect the new state (wiki + sphinx, adobe fw, AE engine, PS engine).

Examples of duplicate definitions

• It looks like the SHOTGUN_ADOBE_NETWORK_DEBUG environment is defined both in the engine and in the framework - we should refactor this to be less leaky. I think we should drop the network_debug flag and the only way to control the debug state is through the SHOTGUN_ADOBE_NETWORK_DEBUG env var, which is only accessed from the fw.
• I am seeing a similar situation for SHOTGUN_ADOBE_PYTHON.