Simplify BoM by using 6x3mm Magnets to Secure the Cover

[jsaintrocc]

Since 6x3mm magnets are more common than the 10x5x3mm magnets it would be nice to provide an alternate cover/wagomount to use those. This would mean the BoM would be 8x 6x3mm magnets and no need to purchase additional 10x5x3mm magnets.