Make HIKvision positive and negative angle landmarks adjustable

[dpq]

HIKvision (at least the model that I have) has this weird gap near zero degrees (and presumably near 180 degrees as well). Positive angles should be calculated from one default/zero angle, negative angles should be calculated from another.

Add 4 more env variables:

LAT_ZLANDMARK_HIK_POSITIVE
LONG_ZLANDMARK_HIK_POSITIVE
LAT_ZLANDMARK_HIK_NEGATIVE
LONG_ZLANDMARK_HIK_NEGATIVE

Landmarks are objects in the center of the camera feed when at 0.0 deg [positive] and -0.0001 [negative] azimuth angles.