checking for 'Level-3_Binned_Data' group in getDecodeQualification

Hi there,

We have made this change to your L3ProductReaderPlugIn. The *getDecodeQualification()* now checks if the group "Level-3_Binned_Data" exists. This is what the *L3BinFileReader* requires.

We discovered the problem because your reader tried to read on of our product we have in our test data set but it failed because the group didn't exist. The product is a "SeaDAS-Level3-a-like" product. and we have our own reader for this.

Would be great if you can take this over into your code repository.