Replaced `visible` with special variable, `$show`

Personal experience has shown me that visibility will most often be inhereted from a parent unless stated otherwise. By using a special variable, it becomes very easy to take an existing module composed of many nested primitives and mark it as hidden for use in aligning child objects. 

`$show` is chosen over `$visible` as I find the variable is used frequently enough to require shortening the length of its name.