feat(authInterceptor): ignore flag and configs

ignoreAuthorization:
Allow <code>$http.post(url, data, { ignoreAuthorization: true })</code>
to ignore certain post requests (for servers that didn't allow
Authorization in cors config)
cache auth:
maintain a reference to <code>auth</code> before injecting again
Merge pull request #77 from gdi2290/patch-2

feat(authInterceptor): ignore flag and cache auth