Added possibility to set drawables programmatically

FlipImageView.java

 public void setFlippedDrawable(Drawable flippedDrawable){
        mFlippedDrawable = flippedDrawable;
        if(mIsFlipped) setImageDrawable(mFlippedDrawable);
    }

    public void setDrawable(Drawable drawable){
        mDrawable = drawable;
        if(!mIsFlipped) setImageDrawable(mDrawable);
    }