Filtered counts on studio performer subpage

[dogwithakeyboard]

Following on from #4162 making a new PR as I managed to make a complete hash of updating to latest develop.

Makes the Performers' scene, image, movie and gallery counts in the Studio > Performers page return the number of scenes etc that the performer has with that studio rather than the total for the performer. On the subpage the counts filters and sorts will use the filtered number.

• Adds a findPerformers resolver to the Studio type which accepts a PerformerFilter and FindFilter, and depth to handle the studio hierarchy.

• Adds a new StudioPerformer type with its own count resolvers.

• Adds a new argument to the makeQuery function to override the normal sorting behaviour when queried though the studio resolver.