`New Profile` should always instantiate with a non-existent profile name

[joaomoreno]

1. Run New Window with Profile > New Profile...
2. Click Create to create a profile called Untitled
3. Run New Window with Profile > New Profile... again
4. Click Create

🐛 Nothing happens

Thoughts:

1. The second untitled profile should've been suggested as Untitled 2 or something
2. The Create and Preview buttons should be disabled if there's any error in the form