Example dApp Fails to Detect if MetaMask is Not Installed

[danforbes]

If a user visits the example dApp without MetaMask installed, the dApp loads in a non-responsive state and there is no indication to the user that anything is wrong. The behavior of the example dApp should be resilient and well-understood for all cases including but not limited to:

• MetaMask is not installed
• Snap is installed
• Snap is installed but out-of-date
• Both MetaMask and Flask are installed, etc...