Improve signup UX

[teyim]

Current behavior

After inputing a team name in step one, the user only discovers that this team name is not available after clicking the finish button in step 3. This user experience is a little poor, since the user will continuessly navigate between the first step and last step and will also have to wait for some time (depending on their network speed) in step 3 before getting that error.

Suggested Behavior

User should see team name availability as they type in the team name. Something similar to typing in a new repo name in Github