Add light sync command

- Only syncs block headers (excludes block bodies, transactions, receipts, and logs)
- Modifies validation window to include the most recent block
- Isolates validation window to the variable defined in the cmd directory (blocks
  have a separate variable defined in the block_repository for determining when
  to set a block as final)

examples/erc20_watcher/every_block/fetcher_test.go

@@ -28,7 +28,7 @@ var _ = Describe("ERC20 Fetcher", func() {
 	blockNumber := int64(5502914)
 
 	infuraIPC := "https://mainnet.infura.io/J5Vd2fRtGsw0zZ0Ov3BL"
-	realBlockchain := geth.NewBlockchain(infuraIPC)
+	realBlockchain := geth.NewBlockChain(infuraIPC)
 	realFetcher := every_block.NewFetcher(realBlockchain)
 
 	fakeBlockchain := &mocks.Blockchain{}

examples/erc20_watcher/every_block/integration_test.go

@@ -58,7 +58,7 @@ var _ = Describe("Everyblock transformers", func() {
 	})
 
 	It("creates a token_supply record for each block in the given range", func() {
-		initializer := every_block.TokenSupplyTransformerInitializer{erc20_watcher.DaiConfig}
+		initializer := every_block.TokenSupplyTransformerInitializer{Config: erc20_watcher.DaiConfig}
 		transformer := initializer.NewTokenSupplyTransformer(db, &blockchain)
 		transformer.Execute()
 

examples/erc20_watcher/every_block/transformers.go

@@ -15,8 +15,8 @@
 package every_block
 
 import (
-	"github.com/vulcanize/vulcanizedb/libraries/shared"
 	"github.com/vulcanize/vulcanizedb/examples/erc20_watcher"
+	"github.com/vulcanize/vulcanizedb/libraries/shared"
 )
 
 func TransformerInitializers() []shared.TransformerInitializer {