R1:c32295aab6d7

Improve resolution process for nonfatal setup issues

Summary:
- When a setup issue is nonfatal (i.e., a warning), instruct the user to edit the value from the web UI instead of using `bin/config`.
- When the user edits configuration in response to a setup issue, send them back to the issue when they're done.
- When an issue relates to PHP configuration, link to the PHP documentation on configuration.
- Add new-style setup check for timezone issues.

Test Plan: Mucked with my timezone config…