Updated the interactive configuration function.

Now it calculates the FUV foreground extinction by connecting to
IRSA and parsing the Schlafly and Finkbeiner (2011) values for
A_B and A_V (CTIO filtres). A_FUV is calculated as

A_FUV = 7.9 E(B-V) = 7.9 (A_B - A_V)

This commit also fixes a problem with astroparse when trying
to parse rvel from Simbad. It now uses rv_value.

To work, this function requires the lattest development version
of astropy, which fixes some problems in the Irsa_Dust module.