DRY-up ToastContainer

[alexrussell]

• Fix broken eslintrc file
• Refactor ToastContainer to DRY-up calls to Animated.timing by:
  • Removing multiple calls to setTimeout by extracting the conditional to a variable
  • Passing references to this.closeToast in the timeout rather than redefining the function's body in the timeout callback
• Save a timeout when fading the toast out by using the Animated.timing completion callback rather than using setTimeout with a 500ms delay.