Add 'last-used' to API tokens

[amberrignell]

User story

As a user that is concerned with security, I would like to see when my API token was last-used, so that I can make sure I am the only one using it.

As a user that is getting rid of old API tokens, I would like to see when they were last used, so that I can assess whether it is safe to delete them.

Details

Add a 'last-used' column to the API tokens table in Profile>API tokens.

Implementation notes

Release notes

User acceptance criteria

• When I create a token, the last-used column says 'never'
• When I make a GET, POST or PUT request with a token, the last-used column gets updated to the time of my request.
• If I make a POST request that has a valid token but invalid data (ex: 400), the last-used time is still updated.

[amberrignell]

Closed by #701