Adds Nightvision Security and Medical HUDs!

This update combines the function of night-vision goggles with Medical and Security HUDS.

Both HUDs include the base cost of the night-vision goggles item, plus additional tech and mineral requirements.
- Silver is required for the medical NVG HUD, with a bio tech requirement of 4.
- Gold is required for the security NVG HUD, with a combat tech requirement of 4.
- The electromagnetic spectrum tech requirement for them both is 5, regular NVG remain at 4.
- Like the standard security HUD, the night-vision version also comes in a lockbox.

*Please note that the night-vision security HUD lacks the flash protection and welder eye damage reduction of the typical HUD sunglasses that most officers wear. As such, officers will need to make a tactical choice on which type to wear!

Sprites by Nienhaus!
![screenshot 2014-04-25 12 06 43](https://cloud.githubusercontent.com/assets/4955510/2821864/b0fd0f82-cf0b-11e3-99f0-04d709c0adde.png)