feat(kanban): use total task count from the api instead of manually calculating it per bucket

This fixes an ux issue where the total count would show a wrong number of total tasks because that was the number of tasks which were loaded at the time. In combination with bucket limits, this caused error messages when the user would attempt to drag tasks into a bucket which appeared not full but was.

src/models/bucket.ts

@@ -14,6 +14,7 @@ export default class BucketModel extends AbstractModel<IBucket> implements IBuck
 	tasks: ITask[] = []
 	isDoneBucket = false
 	position = 0
+	count = 0
 	
 	createdBy: IUser = null
 	created: Date = null