Support Data Importer JSON for import and export

[jexp]

• allow as a source for graph schema (similar to predefined schemas)

• export current graph schema as a data importer JSON

• similar to get schema from text / get schema from data / get schema from example this is option 4

• we need nodeLabels, relationshipTypes, relationshipObjectTypes to extract our relevant schema information from the JSON

 "graphSchema": {
        "nodeLabels": [
          {
            "$id": "nl:1",
            "token": "AccountHolder",
            "properties": [
              {
                "$id": "p:1",
                "token": "accountHolderID",
                "type": {
                  "type": "integer"
                },
                "nullable": true
              },
       "relationshipTypes": [
         {
           "$id": "rt:1",
           "token": "BUSINESS_ADDRESS",
           "properties": []
         },
       "relationshipObjectTypes": [
         {
           "$id": "r:1",
           "type": {
             "$ref": "#rt:1"
           },
           "from": {
             "$ref": "#n:1"
           },
           "to": {
             "$ref": "#n:14"
           }
         },