[FIX] Browse groups will move beyond category

[johnlawsharrison]

Since we are using 'greater than' syntax in Mongo to create browse groups, it is technically possible for the user to scroll past a group

For example:

to get group 'A' we find docs with a artist credit > A with a limit of 200, but this will technically get us artists in group 'B' as well if there are less than 200 artists remaining

This is a server side fix with implications on the frontend.

One approach would be to rewrite our get artists code to impose a 'less than' limit, or to use bucketing instead of pagination