TABDEV-1686. Added authentication logging to jive-ios-sdk.
TABDEV-1686. Switch to use property for delegate member.

Was crashing with a EXC_BAD_ACCESS before. I don't know why. Switching to a property fixed it. I think referencing a weak variable via a struct is bad.
TABDEV-1686. Removed unneeded weakifying in auth callbacks.

Since self was weakified in auth callbacks, the Jive object (self) could get dealloc-ed, which would lead to loss of the logging block objects and (more importantly), the authentication deelgate, which handles the authentication callbacks.