Adds Electric Arm Sprite

Added an animated sprite for the engineering borg's electric arm, replacing the old warning sign that was used for the sprite.

Also made borg mesons/thermals/sechuds/medhuds look slightly different from their human counterparts.

![borgsprites](https://cloud.githubusercontent.com/assets/4349173/2939020/d43bce36-d931-11e3-891a-c6ddb784e016.png)