Generate GO term hierarchy file

[dustine32]

We will produce the child-parent relationship file go_hierarchy.json needed to recreate the GO hierarchy. The file should look like this:

  [
    {"child": "GO:0000009", "parent": "GO:0000030"},
    {"child": "GO:0000014", "parent": "GO:0004520"},
    {"child": "GO:0000014", "parent": "GO:0016788"},
    ...
  ]

As you can see in this example, there can be multiple child-parent entries for the same "child" term. @tmushayahama will use this for the left-side GO term filter.