Minimally adapt kernel to use habitat for dependencies and process supervision

[themightychris]

#46 contains the first approach to integrating emergence
The new approach will be to:

• Continue installing emergence-kernel via npm install -g, so that both new machines can be initialized and old machines updated with the same command
• The kernel will handle installing habitat
  • maybe run the habitat curl|bash when the kernel starts if hab isn't found in the path?
  • maybe use some sort of npm hook to do that from a package.json option when the kernel is globally installed?
  • maybe repackage habitat as an npm package so it can just be a dependency for the kernel that npm handles installing to .bin
• The kernel will automate running hab commands
  • maybe just use a promise-based shell npm package to run hab commands
  • maybe repackage habitat as an npm package and expose async functions for each of the habitat commands we want that take node-ified options
• generate a single json document config for the entire host, consisting of the /emergence/config.json base document with a "sites" key added containing an object mapping each site handle under /emergence/sites/* to the contents of its site.json
• setup the config templates for each plan in https://github.com/JarvusInnovations/Emergence/tree/habitat/service-plans to generate from this shared mega-config tree
  • only the nginx config will loop through the "sites" list
  • we might want to remap services.plugins.myservice in legacy config.json to just services.myservice on load if plugins is detected the only key. Update the code that auto-generates new config.json to skip the plugins subkey going forward
• start the habitat supervisor if needed
• reimplement the start / stop functions for each of kernel-lib/services/* to load+start / stop via hab sup
• query hab sup status for current service status on startup and when requested instead of using pid files and maintaining a started/stopped state internally
• customize health check hooks for each service to do as complete a check as possible for being usable by emergence

[themightychris]

Maybe use mobx for observable kernel state? https://medium.com/@botverse/enjoying-mobx-jsx-and-virtual-dom-621dcc2a2bd5

[themightychris]

Even better: mobx-state-tree