annotate: Give more information in transaction description

Now prints messages like:

        Spent $120.34 on 20/04/2014: Yo Mama's Restaurant Pty Ltd

or

        Earnt $1000.00 on 20/04/2014: Yo Mama's Casino Pty Ltd

As the categorisation is now a correctable guess it's okay to
parameterise the category with the amount spent or earnt.