Wallet usage statistics pipeline

[polymutex]

It would be very useful to have some usage numbers on all wallets. This is an indication of their relative popularity and can be a good sorting signal for the comparison table.

Metrics like:

• Chrome/Firefox extension users (displayed on their respective pages)
• App download numbers (for mobile wallets)
• GitHub repo stars (for open-source wallets)
• Download counts (wherever available)

Tasks:

• Write code that can fetch this data, given sufficient wallet metadata
• Tag existing wallets such necessary metadata
• Write build-time logic that does all the fetching and puts all this info somewhere as part of the build (the site needs to remain statically exportable)

Eventually this data should also be displayed on the wallet comparison table and per-wallet page header, but that's for another issue.