Stack basecamp #322, #325, #323, #324, #316 onto preview

[thomasklemm]

preview stacks submitted-but-unmerged upstream PRs. This adds the next performance / fewer-queries batch.

Order

1. Cache boosts with their message instead of one by one basecamp/once-campfire#322 — cache boosts with their message (APPROVED)
2. Render the boosts a message has preloaded instead of querying them again basecamp/once-campfire#325 — render preloaded boosts instead of querying again (APPROVED; builds on Cache boosts with their message instead of one by one basecamp/once-campfire#322)
3. Count unread rooms for push badges once per batch basecamp/once-campfire#323 — count unread rooms for push badges once per batch (APPROVED)
4. Rewrite a message's search entry only when its body or attachment changes basecamp/once-campfire#324 — rewrite search index only when body/attachment changes
5. List one page of account members at a time basecamp/once-campfire#316 — list one page of account members at a time

Fix on this branch

Upstream basecamp#316 still used <%= "checked" %> on the account settings switch. That fails Roundhouse's bin/rails herb:check. Restored preview's tag.input … checked: form.

Held back

basecamp#326 (reuse pinned push connections) — overlaps lib/web_push/pool.rb with basecamp#323 and still has open review threads.

Already elsewhere

• Our Query sidebar directs and shared rooms separately basecamp/once-campfire#318–Keep bot page totals on rooms.messages_count basecamp/once-campfire#321 stack: Stack basecamp #318–#321 onto preview #1
• Find a direct room with one query instead of checking every one basecamp/once-campfire#310 already covers the old Add members_hash for O(1) direct room lookup basecamp/once-campfire#164 direct-room O(n) lookup