message: add articulation spec to skeleton plugin device descriptor
diff: "lastModified": "",
  "interfaces": {
  "skeleton": {
  - "count": 2
  + "count": 2,
  + "bounded": true
  },
  "tracker": {
  "count": 12
  }
  },
  + "articulationSpec": [
  + {
  + "leftWrist" : {
  + "$data" : {
  + "data" : "tracker/0"
  + },
  + "thumbMetacarpal" : {
  + "$data" : {
  + "data": "tracker/1"
  + }
  + },
  + "indexMetacarpal" : {
  + "$data" : {
  + "data": "tracker/2"
  + }
  + },
  + "middleMetacarpal" : {
  + "$data" : {
  + "data": "tracker/3"
  + }
  + },
  + "ringMetacarpal" : {
  + "$data" : {
  + "data": "tracker/4"
  + }
  + },
  + "pinkyMetacarpal" : {
  + "$data" : {
  + "data": "tracker/5"
  + }
  + }
  + }
  + },
  + {
  + "rightWrist" : {
  + "$data" : {
  + "data" : "tracker/0"
  + },
  + "thumbMetacarpal" : {
  + "$data" : {
  + "data": "tracker/1"
  + }
  + },
  + "indexMetacarpal" : {
  + "$data" : {
  + "data": "tracker/2"
  + }
  + },
  + "middleMetacarpal" : {
  + "$data" : {
  + "data": "tracker/3"
  + }
  + },
  + "ringMetacarpal" : {
  + "$data" : {
  + "data": "tracker/4"
  + }
  + },
  + "pinkyMetacarpal" : {
  + "$data" : {
  + "data": "tracker/5"
  + }
  + }
  + }
  + }
  + ],
  "semantic": {
  "hands": {
  "left": {
  