Usernames are now case-insensitive

This fixes a UX issue, where if you accidentally capitalized a letter
in the username when logging in, it would instead create a new account.

The behavior was confusing, since to the user it looks as if their
characters were deleted or progress was not saved.

In order for this to work, duplicate accounts (e.g. username and USERNAME)
need to be deleted/renamed. The server will *detect* if any duplicates
exist. If any are found, it will direct the server operator to a pruning
script, or they can choose to resolve the duplicates manually.

sql/tables.sql

@@ -1,6 +1,6 @@
 CREATE TABLE IF NOT EXISTS Accounts (
     AccountID    INTEGER NOT NULL,
-    Login        TEXT    NOT NULL UNIQUE,
+    Login        TEXT    NOT NULL UNIQUE COLLATE NOCASE,
     Password     TEXT    NOT NULL,
     Selected     INTEGER  DEFAULT 1 NOT NULL,
     AccountLevel INTEGER NOT NULL,