Generate all-upcase agent IDs of 128 bits

Related to home#724 (closed). Users are getting tangled up with case on agent IDs. We should generate all-upcase agent IDs of 128 bits.

https://nodejs.org/api/crypto.html#crypto_crypto_randombytes_size_callback should work, with 16 bytes of data, to get 128 bits of entropy. Then URL-safe base64 to make it readable, like https://www.npmjs.com/package/urlsafe-base64. Or maybe an encoding that leaves out visually-ambiguous chars like 1 and l, 0 and O?