Add storeCredential and getCredential key value store, store secrets in db

[lalalune]

Right now we're storing twitter credentials and other credentials in character file, as well as in tweet cache for twitter login cookies, and other places.

Instead, we should store secrets and credentials per character

We can add these to the memory manager and database adapters to keep the DB unified

So there are a few different parts to this:

1. Add credential key value store to MemoryManager, keyed by agentId
2. Store and retrieve Twitter cookies from this
3. Add script to store and retrieve secrets by agentId / agentName
4. Add checking to get secrets as priority and fall back to character file secrets

This will enable us to store/recall secrets later in a platform, and keep secrets internal to our database without having to put them in characters.