* Conviction provides ammunition for future cases * Shareholders anxious for closure By Andrew Callus LONDON, Nov 16 (Reuters) - BP stands convicted of the biggest corporate crime in U.S. history, based on the scale of its punishment. Moving on will not be easy. Having agreed to pay $4.5 billion and wear the label of felon, the British oil company will face no further federal criminal charges over the 2010 oil spill disaster. On the downside, lawyers now have extra ammun