Make it more difficult for users to accidentally submit duplicate praise

[mattyg]

See #160

Sometimes users accidentally send the same praise twice.

It might be helpful to automatically notify the user, or ask for confirmation, if they appear to have accidentally sent the same praise twice.

Ways we could identify accidental duplicates:

• exact same text
• exact same sender
• exact same recipients
• createdAt time within 5 minutes

[kristoferlund]

Good idea, adding to future features.