OAuth Support (#53)

Rips out the old auth method, adds OAuth support. Fixes #51.

Tested Platforms:
- [x] Linux
    - [x] Flatpak
    - [x] Native (Nix)
- [x] Android
- [ ] Windows
- [ ] MacOS

Reviewed-on: Nexus/nexus#53

linux/runner/my_application.cc

@@ -23,6 +23,13 @@ static void first_frame_cb(MyApplication* self, FlView *view)
 // Implements GApplication::activate.
 static void my_application_activate(GApplication* application) {
   MyApplication* self = MY_APPLICATION(application);
+
+  GList* windows = gtk_application_get_windows(GTK_APPLICATION(application));
+  if (windows) {
+    gtk_window_present(GTK_WINDOW(windows->data));
+    return;
+  }
+
   GtkWindow* window =
       GTK_WINDOW(gtk_application_window_new(GTK_APPLICATION(application)));
 
@@ -93,7 +100,7 @@ static gboolean my_application_local_command_line(GApplication* application, gch
   g_application_activate(application);
   *exit_status = 0;
 
-  return TRUE;
+  return FALSE;
 }
 
 // Implements GApplication::startup.
@@ -140,6 +147,6 @@ MyApplication* my_application_new() {
 
   return MY_APPLICATION(g_object_new(my_application_get_type(),
                                      "application-id", APPLICATION_ID,
-                                     "flags", G_APPLICATION_NON_UNIQUE,
+                                     "flags", G_APPLICATION_HANDLES_COMMAND_LINE | G_APPLICATION_HANDLES_OPEN,
                                      nullptr));
 }