Human Release v2.6

• Add model cache hander using IndexDB in browser environments
  see config.cacheModels setting for details
• Add additional demos
  human-motion and human-avatar
• Updated samples image gallery
• Allow monkey-patching fetch in NodeJS
  If fetch function is defined, it can be used to load models
  from HTTP/HTTPS URLs regardless of tfjs platform support
• Fix BlazeFace detections when face is partially occluded
• Fix BlazeFace box scaling
• Fix HandTrack tracking when hand is in front of face
• Fix ElectronJS compatibility issues
• Fix body keypoints interpolation algorithm
• Updated BlazePose calculations
• Changes to BlazePose and HandLandmark annotations
• Strong typing for string enums
• Updated TFJS