Handle validation errors consistently

[trex]

We need to display user-input validation errors to the user when they are (or before they) submit a form.

I created a ValidationError component that I am using on the AddGroup form. I want to discuss server validation strategies and make a decision collectively how we want to handle this. The ValidationError component may not be the right strategy 🤷‍♂️.

We should also keep the form populated if they fail validation.

• Handle validation errors
• Form remains populated on validation failure

[trex]

This is related to #50