Add a new random greeting from memory when loading a new character

[wawawario2]

@digiwombat requested:

"Adding onto this concept, I'd really love to see a new greeting generation when loading a new character with no chat backlog. Pick a random recent memory and greet based off that.

For example: It picks a memory where you discussed a film you were planning on watching, character welcomes you back asks if you watched it yet. They could also comment on how long it's been since you last spoke or something to that effect based on timestamps.

Might be useful to add session counts in the db based on when it was last cleared so the character doesn't go back too far. A quick glance at the Extensions docs makes that seem like the hooks would need to be expanded a bit for the idea to be feasible, though."