unity8: initial packaging (!27)

* Mir starts up and is able to display system settings
* x86_64 only for now, because at least ubuntu-app-test did not build
  on aarch64

Based on PureTryOut's work. Getting it to this stage was a huge effort
(as it shows in the package count: 111(!)). See the merge request for
details.

[skip ci]: this won't finish in CI; ollieparanoid made sure that
           everything builds for x86_64.

unity8/location-service/missing_includes.patch

@@ -0,0 +1,12 @@
+diff --git a/include/location_service/com/ubuntu/location/service/permission_manager.h b/include/location_service/com/ubuntu/location/service/permission_manager.h
+index 73b79bd..045a83d 100644
+--- a/include/location_service/com/ubuntu/location/service/permission_manager.h
++++ b/include/location_service/com/ubuntu/location/service/permission_manager.h
+@@ -19,6 +19,7 @@
+ #define LOCATION_SERVICE_COM_UBUNTU_LOCATION_SERVICE_PERMISSION_MANAGER_H_
+ 
+ #include <memory>
++#include <sys/types.h>
+ 
+ namespace com
+ {