Add more popular datasets to graphscope built-in datasets

We have several built-in datasets that can be easily loaded in one-line, located in the dataset directory of Aliyun OSS bucket graphscope, and the corresponding utility function to load them, located in python/graphscope/dataset/. We are planning to enrich the datasets continuously.

There's the procedure to add new datasets:

1. Find a popular and appropriate dataset, adapt the format to property graph if necessary,
2. Put all data files inside a folder, give the folder a meaningful name,
3. Compress the folder, then upload the compressed file together with the original folder to the dataset folder of the OSS bucket. Assume you have a folder named foo/, and two files foo/nodes.csv and foo/edge.csv, after this step, you will have the following file structure in the bucket:

dataset
|-- foo.tar.gz
|-- foo
    |-- nodes.csv
    |-- edge.csv

4. Write the loading function load_foo in a new file named python/graphscope/dataset/foo.py.
5. A corresponding unit test is appreciated!