What is Joe Grand's perspective on the Ledger issue and the hardware wallet hack that he conducted? Please provide a detailed explanation of his views, including the key points he raises, the methodology he employed to hack the hardware wallet, and any insights he offers regarding the security vulnerabilities in the Ledger device. Additionally, describe the potential implications of his findings and the measures that Ledger or other hardware wallet manufacturers could take to address these vulnerabilities and enhance the security of their products.