CLICKbase half-width baseplates

These are half-width options for the Gridfinity CLICKbase baseplate variant. The baseplate units in this remix are 42 x 21 mm. They hold bins on the long sides of each unit only but still have clip connectors on all four sides. The 1 x 1 quarter-size unit, which has clips but does not click, fills the corner between two half-width baseplates.