reformat the way signatures work

Instead of using SignedMessages (which no longer exist), you use a
signature and a message. Additionally, the functions SignObject and
VerifyObject have been added, to help enforce the idea that objects need
to be encoded (according to std siaencoding) and then hashed before they
are signed or verified.
switch rpcs to using messages instead of message pointers
change rpcs port numbers. there will be a new standard for picking port numbers soon