differentiate between user-defined pattern filters and gibber created pattern filters

[charlieroberts]

At one point, I believe there were separate filter categories for pre and post in addition to user-defined / added filters. If this was restored / implemented, we could make it easy for users to remove problematic filters that they've added without having to worry about them removing other critical filters (like note->frequency conversion, or beat->samples, or filters for annotations) that gibber adds automatically.