add additional checks to UI on texture of objects are not visable

[y0014984]

[player, "VIEW", laptop1] checkVisibility [eyePos player, getPosASL laptop1]
lineIntersects [eyePos player, getPosASL laptop1, player, laptop1];

These commands do not work very well, because they are point based and the screen is maybe very large. So depending on the sepected point to check, the display wouldn't be updated even if the player has a good vision on other parts of the screen.

Currently I'm not sure if this will add that much benefit or reduce the network traffic that much.