Fix for broken ECS deployment

[obonobo]

Main branch broken from commit: 942c38c14bad51ace963d5cb0c13c2c0aed05aa1

This is the merge commit for PR: #189

The bug: Root url for the app not working (frontend). APIs unaffected.

The fix:

• Changes to react-router configuration in the AppRouter component
• Small backend change to add the signup route to the ApiRouter