Add Support for Pandas Dataframes in Boxplot

There is no support for pandas dataframes in Boxplot, but there is in the other plots. For example:

```python
from MatPlus import BoxPlot

df = pd.DataFrame({'values': [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]})

# Pass the DataFrame column to BoxPlot
box = BoxPlot(df['values'])
box.plot()
```