Optimize comment pagination in post_id, viewmore

Against a clean seeded DB, reduces `GET /post/1/` from 63 queries to
26 by removing redundancies and slow lazy-loaded queries during
top comment pagination.

Also applies eager loading to /viewmore/ with the expected reduction
from 5*(N comments) queries to ~12/request.

For testing locally, use a newly seeded DB to ensure
Comment.descendant_count is populated.

Ref: #485

files/helpers/comments.py

@@ -1,15 +1,15 @@
 from pusher_push_notifications import PushNotifications
-from files.classes import Comment, Notification, Subscription
+from files.classes import Comment, Notification, Subscription, User
 from files.helpers.alerts import NOTIFY_USERS
 from files.helpers.const import PUSHER_ID, PUSHER_KEY, SITE_ID, SITE_FULL
 from files.helpers.assetcache import assetcache_path
 from flask import g
 from sqlalchemy import select, update
 from sqlalchemy.sql.expression import func, text, alias
-from sqlalchemy.orm import aliased
+from sqlalchemy.orm import Query, aliased
 from sys import stdout
 import gevent
-import typing
+from typing import Optional
 
 if PUSHER_ID != 'blahblahblah':
 	beams_client = PushNotifications(instance_id=PUSHER_ID, secret_key=PUSHER_KEY)
@@ -217,3 +217,16 @@ def comment_on_unpublish(comment:Comment):
 	reflect the comments users will actually see.
 	"""
 	update_stateful_counters(comment, -1)
+
+
+def comment_filter_moderated(q: Query, v: Optional[User]) -> Query:
+	if not (v and v.shadowbanned) and not (v and v.admin_level > 2):
+		q = q.join(User, User.id == Comment.author_id) \
+		     .filter(User.shadowbanned == None)
+	if not v or v.admin_level < 2:
+		q = q.filter(
+			((Comment.filter_state != 'filtered')
+				& (Comment.filter_state != 'removed'))
+			| (Comment.author_id == ((v and v.id) or 0))
+		)
+	return q