Based on issues identified in https://meta.discourse.org/t/improved-bookmarks-with-reminders/144542/20
* Implement the resolvedTimezone() function on the user model where we return the user's timezone if it has been set, or we guess it using moment and save it to the user using an update call if it has not yet been set. This covers the cases of users who do not log out/in often who will not get their timezone set via login. This also makes sure the guess + save is done in a non-obtrusive way not on every page -- only when it is needed.
* Before if a user's timezone was blank when they visited their profile page we were autofilling the dropdown with the guessed timezone from moment. However this was confusing as it would appear you have that timezone saved in the DB when you really didn't. Now we do not autofill the dropdown and added a button to automatically guess the current timezone to make everything more explicit.
Based on reports here https://meta.discourse.org/t/improved-bookmarks-with-reminders/144542
* Because the `userHasTimezone` property was computed and we were checking on an (essentially) global object, ember was not aware that the user timezone had changed because it changed in a different place. instead set the timezone as internal state for the modal on show and base the computed property off of that so it mutates correctly
* The tap-tile components were in the admin folder completely unnecessarily, move them out into the main discourse folder otherwise noone else can use the new bookmarks (icon + text is missing)
* Cosmetic fixes for the bookmark modal
* Do not show "later today" when the later time will be > 5pm
* When a custom reminder time is selected, store it in localStorage. The next time the modal is opened, if the last datetime is > now, then a new tile with "Last" will be shown that lets the user reselect that same time.
* Also add an explicit "No Reminder" option that is selected by default
Add enable_bookmark_at_desktop_reminders site setting default to false a new hidden site setting to hide the "At Desktop" reminder option so we can restrict this further until it is polished.
