Implement data flow map reduce tree construction

[dmgaldi]

Overview

• Bulk of the logic can be found in DataFlowTreeFactory
• A couple of classes were renamed where the only changes are some additional documentation.

Testing

• Ran locally on PRISM study with the following request:

  {
  "filters": [
      {
          "entityId": "EUPATH_0000609",
          "type": "numberRange",
          "variableId": "EUPATH_0000047",
          "min": 3.2,
          "max": 15.4
      },
      {
          "entityId": "EUPATH_0000776",
          "type": "numberRange",
          "variableId": "EUPATH_0000135",
          "min": 0,
          "max": 500.5
      }
  ],
  "outputVariableIds": [
      "OBI_0001169",
      "EUPATH_0000162",
      "EUPATH_0000317"
  ]
  }