* 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`
### UI Changes
If `SiteSetting.enable_bookmarks_with_reminders` is enabled:
* Clicking "Bookmark" on a topic will create a new Bookmark record instead of a post + user action
* Clicking "Clear Bookmarks" on a topic will delete all the new Bookmark records on a topic
* The topic bookmark buttons control the post bookmark flags correctly and vice-versa
Disabled selecting the "reminder type" for bookmarks in the UI because the backend functionality is not done yet (of sending users notifications etc.)
### Other Changes
* Added delete bookmark route (but no UI yet)
* Added a rake task to sync the old PostAction bookmarks to the new Bookmark table, which can be run as many times as we want for a site (it will not create duplicates).
Note: All of this functionality is hidden behind a hidden, default false, site setting called `enable_bookmarks_with_reminders`. Also, any feedback on Ember code would be greatly appreciated!
This is part 1 of the bookmark improvements. The next PR will address the backend logic to send reminder notifications for bookmarked posts to users. This PR adds the following functionality:
* We are adding a new `bookmarks` table and `Bookmark` model to make the bookmarks a first-class citizen and to allow attaching reminders to them.
* Posts now have a new button in their actions menu that has the icon of an actual book
* Clicking the button opens the new bookmark modal.
* Both name and the reminder type are optional.
* If you close the modal without doing anything, the bookmark is saved with no reminder.
* If you click the Cancel button, no bookmark is saved at all.
* All of the reminder type tiles are dynamic and the times they show will be based on your user timezone set in your profile (this should already be set for you).
* If for some reason a user does not have their timezone set they will not be able to set a reminder, but they will still be able to create a bookmark.
* A bookmark can be deleted by clicking on the book icon again which will be red if the post is bookmarked.
This PR does NOT do anything to migrate or change existing bookmarks in the form of `PostActions`, the two features live side-by-side here. Also this does nothing to the topic bookmarking.
Martin Brennan
Martin Brennan