[Decoder/Pose] Get key body connections from optional file

[Decoder/Pose] Get key body connections from optional file

The body connections are added to each keypoint line in the
optional key body listing file.
A space separated number list is expected to describe other keypoints
connected to the current's one.

For example, default pose decoder configuration could be described
as the following:
top 1
neck 0 2 5 8 11
r_shoulder 1 3
r_elbow 2 4
r_wrist 3 1
l_shoulder 1 6
l_elbow 5 7
l_wrist 6
r_hip 1 9
r_knee 8 10
r_ankle 9
l_hip 1 12
l_knee 11 13
l_ankle 12

Signed-off-by: Xavier Roumegue <xavier.roumegue@nxp.com>