Implement mechanism for tracking Layer 3 delegations

[nisnevich]

In L3, we consider a system where every month a person can "delegate" (any better words for this?) a certain amount of points (say, up to 10000) to support activities of other members. The bot may automate this with a command like:

!delegate @nick 2000 to support his monthly football activity

So the bot would

• track the monthly limit for each person, not allowing to "delegate" more than it
• show the remainders on request
• provide analytics