Make sure the focus and blur method always works
Make sure the focus and blur method always works

Currently, when you do not specify a ref string (which is discouraged anyway!), calling focus just crashes for no obvious reason.
This adds a fallback to store the ref trough a callback method to avoid this issue.
kosiakMD/react-native-elements,react-native-community/React-Native-Elements,kosiakMD/react-native-elements,martinezguillaume/react-native-elements