Raise error if there are multiple matches

[paulcsmith]

Similar to AmbiguousMatchError in Capybara

If you do click "@something" and there are 2 or more elements that match, raise LuckyFlow::AmbiguousMatchError

The error message should give pointers on what's going on and how to resolve it. For example:

There were X matches for "#{the_selector}" so LuckyFlow isn't sure which one you meant.

Try this...

  * Use a more specific selector: ".my-wrapper-element #{the_selector}"

Also, add a click_first method to just click the first one