Block categorization (#110)

* Add block categorization (is_final=)

* Add godo task for vulcanizeDB (Example of how everything could work together)

* Add unique constraint on block_number and node

* Add index on block_id for transactions_table

* Add node_id index on blocks table

* Sort transactions returned from FindBlock by tx_hash

* lowercase tx_to, tx_from like etherscan

db/migrations/1513613036_add_is_final_to_blocks.down.sql

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+ALTER TABLE blocks
+    DROP COLUMN is_final;

db/migrations/1513613036_add_is_final_to_blocks.up.sql

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+ALTER TABLE blocks
+    ADD COLUMN is_final BOOLEAN;

db/migrations/1513781105_add_unique_constraint_blocks_node.down.sql

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+ALTER TABLE blocks
+  DROP CONSTRAINT node_id_block_number_uc;

db/migrations/1513781105_add_unique_constraint_blocks_node.up.sql

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+ALTER TABLE blocks
+  ADD CONSTRAINT node_id_block_number_uc UNIQUE (block_number, node_id);

db/migrations/1513783615_add_block_id_index_on_transactions_table.down.sql

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+DROP INDEX block_id_index;

db/migrations/1513783615_add_block_id_index_on_transactions_table.up.sql

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+CREATE INDEX block_id_index ON transactions (block_id);

db/migrations/1513783944_add_node_id_index_on_blocks_table.down.sql

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+DROP INDEX node_id_index;

db/migrations/1513783944_add_node_id_index_on_blocks_table.up.sql

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+CREATE INDEX node_id_index ON blocks (node_id);