Add software sources into submenu (Adding code from PR #382) (#432)

* Add Software Sources option to menu, and do not interrupt main event loop.

usr/lib/linuxmint/mintinstall/mintinstall.py

@@ -899,6 +899,11 @@ def list_header_func(row, before, user_data=None):
         self.refresh_cache_menuitem.set_sensitive(False)
         submenu.append(self.refresh_cache_menuitem)
 
+        software_sources_menuitem = Gtk.MenuItem(label=_("Software sources..."))
+        software_sources_menuitem.connect("activate", self.open_software_sources)
+        software_sources_menuitem.show()
+        submenu.append(software_sources_menuitem)
+
         self.prefs_menuitem = Gtk.MenuItem(label=_("Preferences"))
         self.prefs_menuitem.connect("activate", self.on_prefs_clicked)
         self.prefs_menuitem.show()
@@ -1400,6 +1405,15 @@ def load_landing_apps(self, rcache=None):
         self.load_featured()
         self.load_top_rated()
 
+    def open_software_sources(self,_):
+        # Opens Mint's Software Sources and refreshes the cache afterwards
+        def on_process_exited(proc, result):
+            proc.wait_finish(result)
+            self.refresh_cache()
+        p = Gio.Subprocess.new(["mintsources"], 0)
+        # Add a callback when we exit mintsources
+        p.wait_async(None, on_process_exited)
+
     def should_show_pkginfo(self, pkginfo):
         if pkginfo.pkg_hash.startswith("apt"):
             return True