Add bonus pp to UserStatistics API response object

[ZenoXi]

As far as I can tell, there is no way to get the exact bonus pp a user has since it requires knowing the number of ranked maps a user has set scores on, which also isn't in the response. The only case where it is possible is when a user has <100 scores in their best scores list, but this is very limiting. One use case for knowing bonus pp (which is why I'm requesting this) would be calculating the new user total pp value given some hypothetical score.

Probably just having the number of ranked maps with scores set would be better, since you can easily calculate bonus pp from that, but either would be nice.

[peppy]

We don't store this server-side, so it would be a relatively complex implementation (needs to be cached).