Magicsig::generate is now static

Magicsig::generate is now static

This also fixes a problem with "initial salmon slap", which was a
problem for newly registered accounts which would have their first
salmon slap fail to distribute since there was a problem with Magicsig
keys. Apparently we have to re-read them with importKeys so the
Crypt_RSA objects publicKey and privateKey match later instances of them.

I think it may have been that generate() doesn't specify a signatureMode,
but I leave experimentation of that to the future.