BROR adjustable feet

Adjustable foot for the BROR shelving system. Use foot_simple.stl for a regular BROR leg, and foot_tee.stl for where a pair of BRORs are positioned against one another. Each foot_simple requires one M4 bolt, and each foot_tee requires a pair. For each bolt print one foot_base.stl to stop the bolt scratching your floor.