Encoded DSA public key does not contains the DSA parameters

org.xwiki.crypto.params.cipher.asymmetric.AsymmetricKeyParameters#getEncoded() does not encode the DSA parameters (p, q, g), only y is encoded. This make the DSA key almost useless in the current for of the API, so it is a bug.

The easy fix is therefore to add these parameters in the encoding. On the long term, it should also be useful to not have them, but a way to add them from another source.