Control Panel should indicate Production/Development mode

[alecpm]

The shop control panel should have a clear info box on top indicating whether the site shop is currently in Production or Development mode, with instructions to set the JAZKARTA_SHOP_PRODUCTION as appropriate.

It may make sense to use a finer grained mechanism to turn on Production mode, since the environment variable will naturally affect multiple sites running under the same Zope instance, which may not be desirable.