Implement `Copy` method for `ux.Grid`

[philipc2]

Create a method to either return a shallow or deep copy of a Grid object.

Example

uxgrid = ux.open_grid(grid_path)

# shallow copy: reference to original object 
uxgrid_shallow = uxgrid.copy(deep=False)

# deep copy: new object is initialized with same data 
uxgrid_deep = uxgrid.copy(deep=True)

[erogluorhan]

This has been addressed for deep copy. We can close this and create a new issue for shallow copy only or we can modify this to reflect the need for shallow copy