application: Add CallsSettings class

This makes it easy to access application wide settings.

data/meson.build

@@ -67,3 +67,14 @@ install_data(
     'apps'
   )
 )
+
+install_data('sm.puri.Calls.gschema.xml',
+  install_dir: join_paths(get_option('datadir'), 'glib-2.0/schemas')
+)
+
+compile_schemas = find_program('glib-compile-schemas', required: false)
+if compile_schemas.found()
+  test('Validate schema file', compile_schemas,
+  args: ['--strict', '--dry-run', meson.current_source_dir()]
+  )
+endif