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
* Improve the bookmark mobile on modal so it doesn't go all the way to the edge and the custom datetime input is easier to use
* Improve the rake task for syncing so it does not error for topics that no longer exist and batches 2000 inserts at a time, clearing the array each time
### 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).
Martin Brennan