Live deploy as a nightly version

I've added the live deploy option as a nightly version. This future is enabled by setting the "live-deploy-mode" flag to true.

review @devoncarew @ussuri
The fact from the recent bug reports for CDE is that many/most users don't know or don't pay attentions to the errors in the console. We might to address that problem, too (by intercepting the error messages going to the console and presenting them in a friendlier way), but right here I'd say a simple `spark.showErrorMessage('Error During Live Deployment',  exception: e)` call would be useful.