Set the character set before making a connection

Ideally the character set should be set with the connection, and so this is
exactly what's being done now.

And now the character set code is attempted to be generalised.

lib/database/schema.php

@@ -456,6 +456,16 @@ class Schema
         return true;
     }
 
+    /**
+     * Returns the character set of choice for this DBMS (in practice, UTF-8).
+     *
+     * @return string
+     */
+    public static function charset(): string
+    {
+        return 'UTF8';
+    }
+
     /**
      * Modifies a column in the schema.
      *