Pet attachments: if no file is provided I should be notified when I click attach

[kasugaijin]

Log in as staff and go to a pet photos and files tabs. Click attach and you will see a flash that the upload was successful, even if no attachments were provided. Change this to render an alert saying 'Please select a file to attach'.

Please add the logic to this concern module AttachmentManageable and call in the appropriate action, ideally in a before_action filter. This logic to check there is a file should work as follows when the user clicks the attach button:

• if no attachments provided an, shows the above alert
• if one attachment provided, continues with happy path
• if two attachments provided, continues with happy path

It would be good to add some controller tests for this behaviour.