refs #5614, #5943
- adds a new 'filter' bookshelf plugin which extends the model
- the filter plugin provides handling for merging/combining various filters (enforced, defaults and custom/user-provided)
- the filter plugin also handles the calls to gql
- post processing is also moved to the plugin, to be further refactored/removed in future
- adds tests showing how filter could be abused prior to this commit
6a0f1cf231