Change N/P column in all scripts

[Jason Vander Heiden]

To accommodate adding additional output from IMGT under the --junction flag to MakeDb-imgt:

changeo	imgt
N1_LENGTH	VH: N1-REGION-nt nb, VL: N-REGION-nt nb
N2_LENGTH	N2-REGION-nt nb
P3V_LENGTH	P3'V-nt nb
P5D_LENGTH	P5'D-nt nb
P3D_LENGTH	P3'D-nt nb
P5J_LENGTH	P5'J-nt nb

We need to rename to following in all scripts and documentation:

old name	new name
N1_LENGTH	NP1_LENGTH
N2_LENGTH	NP2_LENGTH

[Namita Gupta]

Double-checked that this is done.