Draft: refactor follows and update_nofications indexing

Based on !819

mock_data/block_data/follow_op/mock_reply_data.json

+{
+  "4999999": {
+    "transactions": [
+      {
+        "ref_block_num": 100000,
+        "ref_block_prefix": 0,
+        "expiration": "2020-03-23T12:08:00",
+        "operations": [
+          {
+            "type": "comment_operation",
+            "value": {
+              "body": "test comment from negative reputation account",
+              "title": "",
+              "author": "wang",
+              "permlink": "test-1",
+              "json_metadata": "{}",
+              "parent_author": "steemrollin",
+              "parent_permlink": "steemit-frequently-asked-questions-faq"
+            }
+          },
+          {
+            "type": "comment_operation",
+            "value": {
+              "body": "test comment from 0 reputation account",
+              "title": "",
+              "author": "awhite",
+              "permlink": "test-2",
+              "json_metadata": "{}",
+              "parent_author": "steemrollin",
+              "parent_permlink": "steemit-frequently-asked-questions-faq"
+            }
+          },
+          {
+            "type": "comment_operation",
+            "value": {
+              "body": "test comment from high reputation account",
+              "title": "",
+              "author": "gavvet",
+              "permlink": "test-3",
+              "json_metadata": "{}",
+              "parent_author": "steemrollin",
+              "parent_permlink": "steemit-frequently-asked-questions-faq"
+            }
+          }
+        ],
+        "extensions": [],
+        "signatures": [
+          ""
+        ]
+      }
+    ]
+  }
+}