Migration with Client Python: Write the example code for loading data into Grakn

[grabl]

This issue was originally posted by @sorsaffari on 2018-09-15 11:30.

Uses the same dataset and mechanism as the example written for the Node.js Client. #### To do: - for each data format: - create and test a Grakn transaction - write the migration mechanism - locate the data file - write the template - construct insert queries - execute insert queries - ensure data is in Grakn - ✅ csv - ✅ xml - ✅ json - ✅ refactor and add comments - ✅ add readme - revise based on feedback - - -