Add first changes to syncing logic

- Adds testing framework
- Breaks out new `NetworkContext` object

beacon_node/beacon_chain/src/lib.rs

@@ -3,6 +3,7 @@ mod beacon_chain;
 mod checkpoint;
 mod errors;
 pub mod initialise;
+pub mod test_utils;
 
 pub use self::beacon_chain::{BeaconChain, BlockProcessingOutcome, InvalidBlock, ValidBlock};
 pub use self::checkpoint::CheckPoint;