Select net has two columns, so we should limit the column width to the
size of the grid. The size should adjust with the window, so we take
the size of the first column as fixed and assign the rest of the grid
width to the second column.
- renamed connectivity.[h|cpp] to connectivity_data [.h|.cpp] so that the file name matches the main class name.
- GetNetItems() now returns a vector instead of a list