Feature/internal audit 5

[cwhinfrey]

• Add TransferRoot rescue function
• Use transferRootCommittedAt instead of transferRootConfirmed
• Inline _withdrawAndAttemptSwap
• Add swapAndSendToL1 convenience function to L2_UniswapWrapper
• Optimism messenger updates
  • A defaultGasLimit was added as a constructor param to the L2_OptimismBridge
• Add new Arbitrum messenger wrapper updated for their new bridge