display a user friendly error message when their session has expired

[crhistianramirez]

Description

Users should now see "Your session has expired. Please log in."

Type of change

• [ x] Bug fix (non-breaking change which fixes an issue)

Checklist:

• [ x] I have performed a self-review of my own code
• [ x] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [ x] I have added tests that prove my fix is effective or that my feature works
• [ x] New and existing unit tests pass locally with my changes
• [ ] I have updated the acceptance criteria on the task so that it can be tested
• [ x] I have verified my contribution works and looks well in Firefox, Safari and Internet Explorer