Rename shape_i_column to shape_i_attr
Rename shape_i_column to shape_i_attr

Rename `shape_i_column` to `shape_i_attr` in
`detect_connections.auto_detect_adjacent_shapes` function.

The `shape_i_attr` name better describes the argument since it indicates
the attribute of each shape SVG element that uniquely identifies the
shape.

wheeler-microfluidics/svg_model