🐛 Fixed all known filter limitations (#10159)

refs #10105, closes #10108, closes TryGhost/Ghost#9950, refs TryGhost/Ghost#9923, refs TryGhost/Ghost#9916, refs TryGhost/Ghost#9574, refs TryGhost/Ghost#6345, refs TryGhost/Ghost#6309, refs TryGhost/Ghost#6158, refs TryGhost/GQL#16

- removed GQL dependency
- replaced GQL with our brand new NQL implementation
- fixed all known filter limitations
- GQL suffered from some underlying filter bugs, which NQL tried to fix
- the bugs were mostly in how we query the database for relation filtering
- the underlying problem was caused by a too simple implementation of querying the relations
- mongo-knex has implemented a more robust and complex filtering mechanism for relations
- replaced logic in our bookshelf filter plugin
- we pass the custom, default and override filters from Ghost to NQL, which then are getting parsed and merged into a mongo JSON object. The mongo JSON is getting attached by mongo-knex.

NQL: https://github.com/NexesJS/NQL
mongo-knex: https://github.com/NexesJS/mongo-knex

packages/bookshelf-pagination/lib/bookshelf-pagination.js

@@ -199,6 +199,16 @@ pagination = function pagination(bookshelf) {
 
                         throw err;
                     });
+            }).catch((err) => {
+                // CASE: SQL syntax is incorrect
+                if (err.errno === 1054 || err.errno === 1) {
+                    throw new common.errors.BadRequestError({
+                        message: common.i18n.t('errors.models.general.sql'),
+                        err: err
+                    });
+                }
+
+                throw err;
             });
         }
     });