Absolute paths and post-deploy webhook

[cjbt]

• Supports absolute paths for
  • Assets (.css)
  • Scripts (.js, .ts)
  • prepareCrosswalk
• Added crosswalkPath to make prepareCrosswalk built into baker.
  • Note: crosswalkPath and prepareCrosswalk cannot both be defined.
• Added webhook
  • only invoked when BUILD_NOTIFICATION_WEBHOOK_URL is populated
  • webhook will post embeds folder contents
• Added embeds folder to example folder