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/trust-store/link_with_libintl.patch

@@ -0,0 +1,20 @@
+diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
+index 32b3632..4661cbc 100644
+--- a/src/CMakeLists.txt
++++ b/src/CMakeLists.txt
+@@ -17,6 +17,7 @@
+ find_package(Qt5Core REQUIRED)
+ find_package(Qt5Qml REQUIRED)
+ find_package(Qt5Quick REQUIRED)
++find_package(Intl REQUIRED)
+ 
+ pkg_check_modules(DBUS_CPP dbus-cpp REQUIRED)
+ pkg_check_modules(DBUS dbus-1 REQUIRED)
+@@ -108,6 +109,7 @@ if (TRUST_STORE_MIR_AGENT_ENABLED)
+   target_link_libraries(
+     trust-prompt
+ 
++    ${Intl_LIBRARIES}
+     Qt5::Core Qt5::Gui Qt5::Qml Qt5::Quick
+     ${Boost_LIBRARIES}
+     ${PROCESS_CPP_LDFLAGS}