zero Rz cross covariance terms

[betaBison]

This pull request zeroes the cross covariance terms between R_z & Z, R_z & R_x, and R_z & R_y when the camera is in 2D mode.

The matrix indexes for the 6x6 covariance matrix from the ROS PoseWithCovariance message for reference:

	x	y	z	R_x	R_y	R_z
x	0	1	2	3	4	5
y	6	7	8	9	10	11
z	12	13	14	15	16	17
R_x	18	19	20	21	22	23
R_y	24	25	26	27	28	29
R_z	30	31	32	33	34	35

Currently only some of the cross-correlation terms are zeroed. A dash represents that the value is left unchanged.

	x	y	z	R_x	R_y	R_z
x	-	-	0	0	0	-
y	-	-	0	0	0	-
z	0	0	1e-9	0	0	-
R_x	0	0	0	1e-9	0	-
R_y	0	0	0	0	1e-9	-
R_z	-	-	-	-	-	-

The new behavior zeroes out the R_z cross correlation terms so you're essentially left with a covariance matrix that's only the X,Y, and Rz diagonal terms and their respective cross-correlation terms with each other.

	x	y	z	R_x	R_y	R_z
x	-	-	0	0	0	-
y	-	-	0	0	0	-
z	0	0	1e-9	0	0	0
R_x	0	0	0	1e-9	0	0
R_y	0	0	0	0	1e-9	0
R_z	-	-	0	0	0	-

[Myzhar]

@betaBison Thank you for the fix