Handle OAuth responses as querystring as well as JSON on Android

[stuartlangridge]

Twitter, for example, returns OAuth token data as a querystring (x-www-form-urlencoded), not as JSON, so signing in breaks as per https://github.com/fullstackreact/react-native-oauth/issues/165. Correct this by catching the JSON parse error and falling back to extracting the parameters we need from the token instead.