More robust error handling on ShowContact.tsx

[wally-yawn]

Currently when the fetchShowContact method is invoked, error handling is seemingly designed to display an error to the user. However in practice some errors, such as clicking on a user that no longer exists, result in the user being kicked back to the login page.

To reproduce:

Navigate to this url, replacing ${backendURL} and $(userId) with valid inputs for your environment and ${contactId} with an invalid input:

${backendURL}users/${userId}/contacts/${contactId}`

This method is called both from the Contacts.tsx and ShowContact.tsx so please be sure to add cypress tests for both.