Added semi robust backfiller logic (still need snapshot tables) (sola…

…na-labs#105)

- Backfiller/Gapfiller v1 prototype

contracts/sdk/gummyroll/accounts/index.ts

@@ -50,7 +50,7 @@ type MerkleRollHeader = {
 };
 
 type MerkleRoll = {
-  sequenceNumber: BN; // u128
+  sequenceNumber: BN; // u64
   activeIndex: number; // u64
   bufferSize: number; // u64
   changeLogs: ChangeLog[];