Add config option to disable automatic account creation

Also moved the acceptallcustomnames setting to the login section where
it belongs.

config.ini

@@ -14,6 +14,9 @@ sandbox=true
 port=23000
 # will all custom names be approved instantly?
 acceptallcustomnames=true
+# should attempts to log into non-existent accounts
+# automatically create them?
+autocreateaccounts=true
 # how often should everything be flushed to the database?
 # the default is 4 minutes
 dbsaveinterval=240