Add option to not exit with esc

[skorokithakis]

I sometimes press Escape while typing as a reflex, and it would be very inconvenient if this exits the presentation while I'm presenting. Could we have an option to disable this key?

[sloria]

If it doesn't add too much complexity to the codebase, I'd be up for reviewing/merging a PR for this.

[skorokithakis]

Will submit one soon, thanks!