models: Use db query to get # of comments and support filter
models: Use db query to get # of comments and support filter

* Use a db query to get the # of comments
* allow to limit the counted comments to the top level
  comments or the replies to a certain comment.

SysTheron/adhocracy,liqd/adhocracy,DanielNeugebauer/adhocracy,phihag/adhocracy,alkadis/vcv,DanielNeugebauer/adhocracy,DanielNeugebauer/adhocracy,DanielNeugebauer/adhocracy,DanielNeugebauer/adhocracy,alkadis/vcv,alkadis/vcv,SysTheron/adhocracy,phihag/adhocracy,alkadis/vcv,phihag/adhocracy,liqd/adhocracy,liqd/adhocracy,phihag/adhocracy,liqd/adhocracy,SysTheron/adhocracy,phihag/adhocracy,alkadis/vcv