Add textual display of images

Printing an image interactively should return a string similar to that of numpy.array.

Compare:

```
In [10]: a
Out[10]: 
array([[0, 0, 0, ..., 0, 0, 0],
   [0, 0, 0, ..., 0, 0, 0],
   [0, 0, 0, ..., 0, 0, 0],
   ..., 
   [0, 0, 0, ..., 0, 0, 0],
   [0, 0, 0, ..., 0, 0, 0],
   [0, 0, 0, ..., 0, 0, 0]], dtype=uint8)

In [11]: img
Out[11]: <Halcon.Image at 0xed5348>
```
