Plotting error box

[lmichel]

The API plotting catalogues could be enable to plot individual error boxes for any plotted source.

The API could look like ( just an example, not a requirement)

aladin.plotCatalogue(cat_url, ra_col, dec_col,  error_columns=[err_columns]);

error_columns is an array which dimension denotes the type of error:

• err_columns=[pos_err]: plots a circle with the value of the column pos_err as radius.
• err_columns=[pos_ra, pos_dec]: plots a vertical ellipse with the value of the column pos_ra and pos_dec as axes.
• err_columns=[major_axis, minor_axis, angle]: plots an ellipse with major_axis and minor_axis as axes oriented following angle from the east of the North (convention)