Install resource & serializer project templates again

Also using non-deprecated install dir variable now.

Was accidentally disabled in 854e4d35

templates/CMakeLists.txt

-set(apptemplate_DIRS
-    akonadiresource
-    akonadiserializer
+kde_package_app_templates(
+    TEMPLATES
+        akonadiresource
+        akonadiserializer
+    INSTALL_DIR ${KDE_INSTALL_KAPPTEMPLATESDIR}
 )
-
-#kde_package_app_templates(TEMPLATES ${apptemplate_DIRS} INSTALL_DIR ${KDE_INSTALL_KTEMPLATESDIR})