toaster: Don't HTTP cache ToasterTable responses

toaster: Don't HTTP cache ToasterTable responses

Django allows generated pages to be cached by default by the
browser. This can result in stale data displaying for some pages.

Instead, disable HTTP caching of ToasterTable responses, so that
each time a ToasterTable view is displayed, its data is
refreshed. This carries a performance penalty, but ensures that
ToasterTable views (e.g. compatible layers) are correctly
refreshed if the user navigates their history with forward/back.

[YOCTO #7660]

Signed-off-by: Elliot Smith <elliot.smith@intel.com>
Signed-off-by: Michael Wood <michael.g.wood@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>