[Feat] Improve APIs of the Spark library to be more concise for easily importing/exporting/transforming data at the graph level

[acezen]

Is your feature request related to a problem? Please describe.
as title

Describe the solution you'd like
Proposal TBF

[acezen]

Read GAR file to DataFrames

object GraphReader {
     /*
      * Input:  graph yaml path
      * Output: vertex DataFrames and edge DataFrames
      * /
     def read(graph_yaml_path): Pair[Map[String, DataFrame], Map[String, Map[String, DataFrame]]]

     /*
      * Input:  graph info
      * Output: vertex DataFrames and edge DataFrames
      * /
     def read(graph_info): Pair[Map[String, DataFrame], Map[String, Map[adj_list_type, DataFrame]]]
}

Write a set of DataFrames to GAR files

object GraphWriter {
     /*
      * Input:  graph yaml path and a set of DataFrames
      * Status:  success or fail
      * /
     def write(graph_yaml_path,  vertexDataFrames: Map[String, DataFrame], edgeDataFrame: Map[String, DataFrame]): Status 
     
     /*
      * Input:  graph info and a set of DataFrames
      * Status:  success or fail
      * /
     def write(graph_info, vertexDataFrames: Map[String, DataFrame], edgeDataFrame: Map[String, DataFrame]): Status 
}

Transform graph from one type of GAR to another type of GAR

object GraphTransFormer {
     /*
      * Input:  source and dest graph yaml path
      * Status:  success or fail
      * /
     def transform(source_graph_yaml_path, dest_graph_yaml_path): Status
     
     /*
      * Input:  source and dest graph info
      * Status:  success or fail
      * /
     def transform(source_graph_info, dest_graph_info): Status 
}

[acezen]

Solved by pull requests #113 #114