Add parameter forceDismiss to dismissActiveNotification method

Add ```+ (BOOL)dismissActiveNotification:(BOOL)forceDismiss``` method in order to dismiss the message even if it is not fully displayed.

Here is the use case.

We first display a message showing that we are loading data, and then data comes before the animation has finished. At this moment, we want to force it to dismiss the loading message even if it is not fully displayed.