Agg evicting queue

Deprecates #1282 and solves #1214 and #1216.

Behaviour is as follows:
 * Users are free to download
 * If an IP address is "abusing" us with too many aggregator downloads, it gets penalized with a captcha
 * `trustedClients` in configuration can always download without a captcha
 * `maxAggregatedDownloadsInTenMinutes` set to 2 by default (configurable)
This is a completely generic class, hence the templates. Nothing to do with the portal application. This can potentially be reusable, I'm not sure for what yet.

Alternatively I was thinking about allowing only a ctor where this value is specified.