1.6 patch - graphic improvements

- Overhauled every materials and particle effects with custom light shader and retro dithering.

- Added more details to the pilot and infantries' models.

- added clouds on sky.

- replaced stock unity shadow and fog with custom dithered versions.

- Added basic Day / night cycle. AI units without sight devices get slight FOV and spot range nerf at night.

- Added Night vision goggles.

- Added Infra-Red landing light.

- Added more distinctive characteristics to DTV and IR screen with Level and Gain adjustment knobs.

At day time, IR camera gets excessive heat from both the unit and ground, DTV is more useful for finding targets with some extra contrast. 

At night time, IR can see everything regardless of light.

- Optimized terrain model.

my next objective is overhauling UI, some more graphic improvements, and adding the first attack helicopter unit - Mi-24 Hind.