These stocks are built for the long run.The conventional wisdom is that there are two important aspects of timing in investing: when to buy a stock and when to sell it. But are there some stocks that allow you to eliminate the selling part?Three Motley Fool contributors think the answer to this question is a resounding "yes." Here's why they view AbbVie (ABBV 0.10%), Eli Lilly (LLY -1.21%), and Vertex Pharmaceuticals (VRTX 1.40%) as healthcare stocks to buy and hold forever.The key to longevityKeith Speight ...