fix some bugs that the some frequent-patterns are not found.
Now the output form is:
薯片 5 牛奶 6
薯片 4 面包 5 牛奶 6
面包 3 鸡蛋 4 牛奶 6 薯片 4
add new data structure for mFrequentPattern which is the return value from Step2to3
Step7 to 8 will calculate the "Real Frequent Pattern" in the following commits.