Changes in notifying about new releases.

- Unified preferences settings. version_check option is replaced with notify_release that has 3 states.
- fixed logic when show notification based on version string.
- notification shows released version
- dialog notifying new version is never showing if external updater is running.
Escape quotes inside path to external updater

src/libslic3r/AppConfig.cpp

@@ -71,8 +71,6 @@ void AppConfig::set_defaults()
         if (get("drop_project_action").empty())
             set("drop_project_action", "1");
 
-        if (get("version_check").empty())
-            set("version_check", "1");
         if (get("preset_update").empty())
             set("preset_update", "1");