Rework atmospheric post-processing effect to use JSON technique description

[TheMostDiligent]

All rendering techniques are currently defined in the code, and there is a lot of them. The new JSON parsing system should allow moving all technique description to the JSON file. This is a good place to test the system.

Some open questions:

• How fast is parsing JSON descriptions at run-time
• How to combined run-time specific details (e.g. macros) with JSON description