This PR allows a Wildbook URL to a secured endpoint to be entered and then redireted back to after login.

For example, /appadmin/dataIntegrity.jsp is secured, and a public request to it should be redirected to /react/login/ before returning the user to /appadmin/dataIntegrity.jsp.

PR fixes #675

Changes

• Part 1: @JasonWildMe adds the "redirectURL" parameter to Login.java's returned JSON payload
• Part 2: @erinz2020 ensures /react/login/ page does not make any calls to the backend Java
  • remove call to /Collaborate if user is not yet logged in. This interferes with our ability to get the redirect URL.
  • remove call to /UserGetNotifications if user is not yet logged in. This interferes with our ability to get the redirect URL.
• Part 3: @erinz2020 If JSON payload response from Login includes a "redirectUrl" value (e.g., "/appadmin/dataIntegrity.jsp"), redirect to that URL.
• Part 4: @erinz2020 add a spinner on login button to display the status of loading since redirecting might take time

some test points:

1. login/logout normally
2. access protected jsp pages in logged out state, e.g. /individualSearchResults.jsp?username=test etc
3. access protected react pages in logged out state, e.g. /react/encounter-search?username=test&state=unapproved
4. access url that contains searchQueryId, e.g. encounters/thumbnailSearchResults.jsp?searchQueryId=8cdb3e02-e199-4322-bf80-180168bd1b35&regularQuery=true
5. access url that contains hash