Add check on use of recursive embedded fields and throw exception

[andyjefferson]

We do not support embedding fields recursively. For a 1-1/N-1 this would mean that the fields of the object are embedded, and then same for the related object, and so on ... resulting in infinite columns to add. For 1-N/M-N this would mean that we get a join table embedding the normal fields of the embedded object, then another join table, and so on. Check this at metadata load and throw an exception