Launch challenge confirmation changes

[jmgasper]

Use challenge name

On the initial popup, let's use the challenge name input by the user on the popup:

We'll change the text to say Do you want to launch <challenge type> challenge "<challenge name>", like Do you want to launch Code challenge "My test challenge"?

Change Saving to Launching

When the user clicks Confirm, we should do two things:

1. Disable the Cancel button (even if it is disabled already, it's look doesn't change, so we need to visually dim it`
2. Change Saving... to Launching...