This page demonstrates the Copy Down plug-in.
This dynamic action plug-in provides support for up and down arrow keys to navigate a tabular form. Furthermore Shift Up and Shift Down copy the value of a cell to the previous or next row. For copying select list values use Ctrl Shift C.
The plug-in that can be downloaded from the plug-ins section of apex.world
The plug-in functions both for Apex 5.0 and 5.1.
More information is found on this blogpost