WIP: experimental session checker; redirect when session timesout

[alx652]

Note this PR is not ready to merge, even assuming the code logic is good.
There are some configs/files that should be leaned up before merging.

This follows from a request from IDMP to redirect when a session is not longer valid.

The component checks whoami at some regular interval. If there is no user, the either:

redirects to login page (disabled for now)
external url
or makes an alert box.

sample configuration

 "logoutRedirectUrl": "https://google.com",
  "unauthorized": { 
    "link": "https://google.com",
    "message": "You are not authorized to access this resource.<br>Check this link. Login, or use the contact email to request access.",
    "redirectToHome": true,
    "redirectUrl": "https://google.com"
  },
  "sessionChecker": {
    "interval": "1",
    "check": true,
    "redirectUrl": "https://google.com",
    "alertMessage": "There's not a valid session."
  },
  "apiBaseUrl": "http://localhost:8081/",