[Enhancement] Grab user data on loading the guild, instead of on startup

[doqfgc]

As it currently works, dline grabs the guilds' user data on startup, which directly results in startups being a drag for users with many servers (say, the maximum of 100), or servers with many users (say, at least 25,000).

Unsure about how it would implement, but startup performance may be greatly improved if user data was loaded upon invoking a /guild rather than on startup.

For current reference, it takes about 5-10 minutes for dline to start up on my main account (100 servers, 2/3 servers with >10,000 users).