Sync the Gateway configuration with a remote location

[ddragosd]

This PR introduces the capability for the Gateway to sync its configuration with a remote folder in the cloud such as Amazon S3, Google Cloud Storage, IBM Cloud Object Storage, Dropbox, and many others. The configuration is monitored for changes, and when a file is changed, the Gateway is reloaded automatically. This is very useful to gracefully update the Gateway on the fly, without impacting the active traffic; if the new configuration is invalid, the Gateway doesn't break, running with the last known valid configuration.

See the updated README for more details.

Other changes:

• [x] Updated the existing /health-check endpoint to also print information on the config, such as when it was last updated, or when was the Gateway last reloaded:

  {
  "lua_version": "LuaJIT 2.1.0-beta3",
  "status": "API-Gateway is running",
  "config": {
  "lastChangeDetected": "2018-04-24T20:44:59.6466131Z",
  "lastReload": "2018-04-24T20:45:00.653188Z",
  "status": "OK",
  "lastSync": "2018-04-24T20:47:52.1896511Z"
  }  
  }

Types of changes

• [x] Enhancement or new feature (adds new functionality).

[mhamann]

Nice enhancement!

[ddragosd]

thanks @mhamann !