fix #1997 (#2088)

* Fix #1997 (allow the use of an external file for the email blacklist)
* Change config key names for blacklist (compatibility break)
* Accept globs rather than regexes for blacklist by default
* Blacklist comparison is now case-insensitive

traditional.yaml

@@ -391,8 +391,13 @@ accounts:
             #     username: "admin"
             #     password: "hunter2"
             #     implicit-tls: false # TLS from the first byte, typically on port 465
-            blacklist-regexes:
-            #    - ".*@mailinator.com"
+            # addresses that are not accepted for registration:
+            address-blacklist:
+            #    - "*@mailinator.com"
+            address-blacklist-syntax: "glob" # change to "regex" for regular expressions
+            # file of newline-delimited address blacklist entries in the above syntax;
+            # supersedes address-blacklist if set:
+            # address-blacklist-file: "/path/to/address-blacklist-file"
             timeout: 60s
             # email-based password reset:
             password-reset: