refactor: Make Args less of a singleton (#5041)

This means it's no longer a singleton, and its lifetime is bound to our application.
This felt like a good small experiment to see how its changes would look
if we did this.
As a shortcut, `getApp` that is already a mega singleton keeps a
reference to Args, this means places that are a bit more difficult to
inject into call `getApp()->getArgs()` just like other things are
accessed.

src/widgets/settingspages/PluginsPage.cpp

@@ -53,7 +53,7 @@ PluginsPage::PluginsPage()
             this->rebuildContent();
         });
         groupLayout->addRow(box);
-        if (getArgs().safeMode)
+        if (getApp()->getArgs().safeMode)
         {
             box->setEnabled(false);
             auto *disabledLabel = new QLabel(this);
@@ -197,7 +197,7 @@ void PluginsPage::rebuildContent()
                              this->rebuildContent();
                          });
         pluginEntry->addRow(reloadButton);
-        if (getArgs().safeMode)
+        if (getApp()->getArgs().safeMode)
         {
             reloadButton->setEnabled(false);
         }