Pick the completion when user hits right arrow
Pick the completion when user hits right arrow

Closes #385.

jdfreder/nteract,jdetle/nteract,nteract/nteract,captainsafia/nteract,rgbkrk/nteract,nteract/nteract,jdetle/nteract,nteract/nteract,nteract/composition,captainsafia/nteract,captainsafia/nteract,jdfreder/nteract,jdfreder/nteract,rgbkrk/nteract,0u812/nteract,0u812/nteract,jdetle/nteract,0u812/nteract,nteract/nteract,nteract/nteract,temogen/nteract,nteract/composition,captainsafia/nteract,0u812/nteract,temogen/nteract,nteract/composition,temogen/nteract,jdfreder/nteract,jdetle/nteract,rgbkrk/nteract,rgbkrk/nteract,rgbkrk/nteract