bitbake: toaster: enable admin interface on select models

bitbake: toaster: enable admin interface on select models

We enable the admin interface in Toaster.

We add admin models for Build Environments (where the
sysadmin can configure where the builds take place)
and for Layer Sources (marking the upstream provider
for layer information).

The admin interface and associated data are enabled
only for the MANAGED version.

(Bitbake rev: 6618613c9210fb44d36d90f5f2404b435f10dfc8)

Signed-off-by: Alexandru DAMIAN <alexandru.damian@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>