use MongoDB aggregation framework to sort crits and art without tracking likes and crits totals on the data itself

[dierat]

Right now the crits data has a property called 'likesNum' that needs to be incremented with each like, and the art data has a 'critsNum' property that needs to be incremented with every crit added to it so that we can sort this data based on those properties easily. We should be able to implement this using the MongoDB framework and then remove these extra properties.