Add ERC20 token watcher example

- starting with the totalSupply function
- sets contract config on transformer by passing it into the transformer
initializer
- handles block records with the same number for different nodes for both creating token_supply records, and finding missing blocks

db/migrations/1528317902_create_token_supply_table.down.sql

@@ -0,0 +1 @@
+DROP TABLE token_supply;

db/migrations/1528317902_create_token_supply_table.up.sql

@@ -0,0 +1,9 @@
+CREATE TABLE token_supply (
+  id            SERIAL,
+  block_id      INTEGER NOT NULL,
+  supply        DECIMAL NOT NULL,
+  token_address CHARACTER VARYING(66) NOT NULL,
+  CONSTRAINT blocks_fk FOREIGN KEY (block_id)
+  REFERENCES blocks (id)
+  ON DELETE CASCADE
+)