allow configuring tooltip for interactive guideline

[pgrm]

When defining valueFormatter for the tooltip in interactive guideline, than it needs to be done recursively, hence:

} else if (key === 'tooltip') {
  configure(chart[key], options[key], chartType);
}

[pgrm]

btw, in order for this to work, novus/nvd3#1247 also needs to be addressed in nvd3, as I've changed it here: https://github.com/grmanit/nvd3/commit/23be42942d8c6c06cd679d2a6cbb8e033846d7e4

[krispo]

Thanks! I'll update this a bit.