Move Bank to its own crate

Also:
* counters.rs to solana_metrics
* genesis_block.rs to solana_sdk

sdk/src/lib.rs

@@ -4,6 +4,7 @@ pub mod budget_expr;
 pub mod budget_instruction;
 pub mod budget_program;
 pub mod budget_transaction;
+pub mod genesis_block;
 pub mod hash;
 pub mod loader_instruction;
 pub mod loader_transaction;