Implementation of Tizen SSO APIs

Implementation of SSO APIs as per widl file https://code.google.com/p/accounts-sso/source/browse/widl/signon.widl?repo=libgsignon-glib

Backend that provides core functionality is gSSO and more information about that
component could be found at https://01.org/gsso
What about `identities_.insert(std::make_pair(jsid, identity_ptr));`
with this you don't have to typedef `IdentityPair`