NRF52840 DK Holder

Minimalistic holder for NRF52840 DK that avoids the awkward stance when laying on a table due to the battery holder underneath. This holder makes it sit flat and easier to plug in usb cables into and genrally nicer to work with. Its worth nothing that it stays completely flat even when pushing the outermost button (tested with the tall no pigs version). I have made 4 different files, two completely without pigs and only M3 screw mounting and two with a mix of pigs and M3 screws. The other difference is how tall they are raised from the table one is just tall enough to stay flat on the table and the other one is taller than that where the board will sit at a height of around 20mm from the table.