Fix 0011400: Increase default $g_view_configuration_threshold

By default, $g_view_configuration_threshold is currently set to
DEVELOPER. This option should really be changed to have a default of
ADMINISTRATOR, as the configuration of MantisBT can contain sensitive
information.

There won't be impact to current installations, as users at DEVELOPER
level have no links whatsoever in the UI to the adm and manage pages
of MantisBT.