Add demo boolean field on club & athlete.
Support demo accounts login through one click.
Limit club actions for demo trainer.
Add cool script to build some demo sessions using existing names.
Add celery task to build demos every day.
Remove plans link.
Add a button on front page for demo.
Support demos for athlete & trainer, closes #35.
Invite now work using recipient email. Account creation in workflow.
Show invite message for existing accounts.
Redirect on login with invite to club creation.