The main thrust of this PR is to take all the conditional checks based on the `enable_bookmarks_with_reminders` away and only keep the code from the `true` path, making bookmarks with reminders the core bookmarks feature. There is also a migration to create `Bookmark` records out of `PostAction` bookmarks for a site.
### Summary
* Remove logic based on whether enable_bookmarks_with_reminders is true. This site setting is now obsolete, the old bookmark functionality is being removed. Retain the setting and set the value to `true` in a migration.
* Use the code from the rake task to create a database migration that creates bookmarks from post actions.
* Change the bookmark report to read from the new table.
* Get rid of old endpoints for bookmarks
* Link to the new bookmarks list from the user summary page
* This PR changes the user activity bookmarks stream to show a new list of bookmarks based on the Bookmark record.
* If a bookmark has a name or reminder it will be shown as metadata above the topic title in the list
* The categories, tags, topic status, and assigned show for each bookmarked post based on the post topic
* Bookmarks can be deleted from the [...] menu in the list
* As well as this, the list of bookmarks from the quick access panel is now drawn from the Bookmarks table for a user:
* All of this new functionality is gated behind the enable_bookmarks_with_reminders site setting
The /bookmarks/ route now redirects directly to /user/:username/activity/bookmarks-with-reminders
* The structure of the Ember for the list of bookmarks is not ideal, this is an MVP PR so we can start testing this functionality internally. There is a little repeated code from topic.js.es6. There is an ongoing effort to start standardizing these lists that will be addressed in future PRs.
* This PR also fixes issues with feature detection for at_desktop bookmark reminders
* This PR implements the scheduling and notification system for bookmark reminders. Every 5 minutes a schedule runs to check any reminders that need to be sent before now, limited to **300** reminders at a time. Any leftover reminders will be sent in the next run. This is to avoid having to deal with fickle sidekiq and reminders in the far-flung future, which would necessitate having a background job anyway to clean up any missing `enqueue_at` reminders.
* If a reminder is sent its `reminder_at` time is cleared and the `reminder_last_sent_at` time is filled in. Notifications are only user-level notifications for now.
* All JavaScript and frontend code related to displaying the bookmark reminder notification is contained here. The reminder functionality is now re-enabled in the bookmark modal as well.
* This PR also implements the "Remind me next time I am at my desktop" bookmark reminder functionality. When the user is on a mobile device they are able to select this option. When they choose this option we set a key in Redis saying they have a pending at desktop reminder. The next time they change devices we check if the new device is desktop, and if it is we send reminders using a DistributedMutex. There is also a job to ensure consistency of these reminders in Redis (in case Redis drops the ball) and the at desktop reminders expire after 20 days.
* Also in this PR is a fix to delete all Bookmarks for a user via `UserDestroyer`
