Daily stacked and spent summary notifications

[huumn]

This has been requested many times.

Stackers want an overview of how much they earned relative to spent.

This shouldn't be too hard to do and can be pretty minimal to start. We'd just grab user_stats for the prior day and make sure to add any rewards that were just given out (at midnight), then the notification could say "you stacked X sats and spent X sats."

[huumn]

I personally want this so I can try to spend as much as I stacked every day.