Tough to determine whether the master signer for account is re-enabled or just updated based upon operation result and meta

[nullstyle]

Similar to #711, I am having trouble differentiated between when the master signer for an account is re-enabled versus when it is simply having it's weight updated.

Ideally, we would add some info to the SetOptionsResult object to specify how the master signer was affects in this operation, if at all.

As a proposal, I would say we should add a new enum to the XDR defs:

enum SignerChange {
  SIGNER_CHANGE_ADDED = 0,
  SIGNER_CHANGE_UPDATED = 1,
  SIGNER_CHANGE_REMOVED = 2
};

Then SetOptionsResult would become something like:

union SetOptionsResult switch (SetOptionsResultCode code)
{
  case SET_OPTIONS_SUCCESS:
     struct {
       SignerChange *masterSignerChange;
       SignerChange *signerChange;
    } success;
  default:
      void;
  };