This commit introduces a query mechanism to obtain E(B-V) reddening

values (query_reddening.sl). Furthermore, photometric_table was modified
to incoorporate full compatibility for reddening data. Reddening data
can be queried as a function based of a photometric_table
(table.query_reddening()), it can be written (table.write()) together with RA and DEC as
metadata of a photometric_table and can, of course, be read again
(table.read()). Furthermore, reddening data is now per default also
collected in a query_photometry call.