Add a structure that lets you define a template URL per layer to be
shown per comparison recipe. For example, you could use this to define a
URL template to link to the upstream summary page for the package (e.g.
Fedora's page for the acl package is at
https://apps.fedoraproject.org/packages/acl, so you would use
https://apps.fedoraproject.org/packages/%pn% as the template and then
this would be shown for every package).
Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
