Test new gsettings api

g_settings_get_user_value and g_settings_get_default_value
are now covered.
Improve test coverage for gsettings
Improve test coverage for GSubprocess
Improve test coverage for GHashTable
Improve GKeyFile test coverage
Improve GNotification test coverage
Improve search utils test coverage

This adds test cases for the Turkish i.
Improve GSettings test coverage

This covers some more GSettingsSchemaKey api.
Generate overview images for coverage

lcov has the options to generate overview images for each source
file with the --frames option. Lets try this.
Improve GSimpleActionGroup test coverage

Add a case that overwrites an existing action.