Review and update UCD notebook

[tomdonaldson]

While updating table and column names in the UCD notebook, I noticed that a few things were not correct. For example,
the cell containing

ra_name=[c.name for c in columns if c.ucd and 'pos.eq.ra' in c.ucd][0]
dec_name=[c.name for c in columns if c.ucd and 'pos.eq.dec' in c.ucd][0]
ra_name,dec_name

and the subsequent text are wrong. The text says that UCD was unique, but it just appeared to be because of the [0] in the code.

Some subsequent cells have no output, so probably aren't demonstrating what was intended.