[YT Search] No results if items is not in response

When a query results of 0 items, the key items is not present in the
api_response dictionary, raising a KeyError.

Intead, look for the key and call trouble if it's not present.
Merge pull request #715 from joksnet/no_video_results

[YT Search] No results if items is not in response
Merge remote-tracking branch 'origin/API_YT_playlists'
Do not user upper-case for non-constants
fix tests in Python3, and make them parallelizable
Don't be too clever (Fixes Python 3)