Longer Lk5 - Tool Holder

Remix of [Ender 3 - Tools Holder](https://www.thingiverse.com/thing:5835010) by skmiedg, adapting the attachment to Longer Lk5 top rail. Due to the diagonal supports the external attachment of the original won't match, so I made one that slips inside the rail on the two sides of the screw, replacing the endcap.

FreeCAD source included, but don't hold your breath - the original is stil an STL mesh; the most "parametric thing" you can use it for is the attachment bars, to attach something else in place of that tool holder.