Tax as symbol in DB

It used to be an index, now it is a symbol (in ruby, string
in MongoDB).

Signed-off-by: Zeljko <zeljko@zwr.fi>
Code cleanup

Remove sample code removed
(see http://stackoverflow.com/questions/23977594), clean not
needed rake task (did it arrive with newner mongoid? and
some ugly puts).

Signed-off-by: Zeljko <zeljko@zwr.fi>