Make all api fields snake_case (#105)

Change all snake/camelCase mix and match to camelCase everywhere

Fix conversion to not interfer with service interceptors

Add dynamic conversion between camelCase and snake_case to services

Co-authored-by: kolaente <k@knt.li>
Reviewed-on: https://kolaente.dev/vikunja/frontend/pulls/105

src/models/taskAssignee.js

@@ -9,8 +9,8 @@ export default class TaskAssigneeModel extends AbstractModel {
     defaults() {
         return {
             created: null,
-            user_id: 0,
-            task_id: 0,
+            userId: 0,
+            taskId: 0,
         }
     }
 }