Allow GET applications route to optionally return only processed/unprocessed applications

Similar to to the way the GET route for badges allows you to query for only archived or non-archived badges, this allows the GET applications route to optionally return only processed or non-processed applications.

I opted to keep the default such that all applications (even already processed ones) are returned in order to keep things working as they are for people that choose not to use this functionality, though I suspect that in the vast majority of cases, people will want only the non-processed badges returned.