Remove depenance on external libs for unique id

I didn't want to have to include "labix.org/v2/mgo/bson" and "github.com/mikespook/golib" in my project just for this little function, so I added a simple auto increment id generator. The code using the IdGenerator interface made it easy.

Note: the id needs to unique across currently running jobs, so I feel the method used below is adequate.