Add ledger_state and ledger_manger struct

src/ledger_manager.rs

+use crate::crypto::hash::H256;
+
+use std::collections::HashSet;
+
+//state required by ledger-manager
+pub struct LedgerManagerState {
+    pub last_level_processed: u32,
+    pub proposer_blocks_processed: HashSet<H256>,
+    pub leader_sequence: Vec<H256>,
+    pub tx_confirmed: HashSet<H56>,
+}
+
+//ledger-manager which will periodically loop and confirm the transactions 
+pub struct LedgerManager {
+    pub ledger_manager_state: LedgerManagerState,
+}
\ No newline at end of file

[bmjain2]

leader_sequence could be a HashMap, Vec also works.