Avoid using reserved identifier in the global namespace

apps/launcher/datafilespage.cpp:762:12: warning: declaration uses identifier '_reloadCellsMutex', which is reserved in the global namespace [bugprone-reserved-identifier]
std::mutex _reloadCellsMutex;
           ^~~~~~~~~~~~~~~~~
           reloadCellsMutex

apps/openmw/mwgui/journalwindow.cpp:86:103: warning: declaration uses identifier '_sender', which is reserved in the global namespace [bugprone-reserved-identifier]
        void adviseButtonClick (char const * name, void (JournalWindowImpl::*Handler) (MyGUI::Widget* _sender))
                                                                                                      ^~~~~~~
                                                                                                      sender

apps/openmw/mwgui/journalwindow.cpp:92:100: warning: declaration uses identifier '_sender', which is reserved in the global namespace [bugprone-reserved-identifier]
        void adviseKeyPress (char const * name, void (JournalWindowImpl::*Handler) (MyGUI::Widget* _sender, MyGUI::KeyCode key, MyGUI::Char character))
                                                                                                   ^~~~~~~
                                                                                                   sender

apps/launcher/datafilespage.cpp

@@ -759,13 +759,13 @@ void Launcher::DataFilesPage::slotAddonDataChanged()
 }
 
 // Mutex lock to run reloadCells synchronously.
-std::mutex _reloadCellsMutex;
+static std::mutex reloadCellsMutex;
 
 void Launcher::DataFilesPage::reloadCells(QStringList selectedFiles)
 {
     // Use a mutex lock so that we can prevent two threads from executing the rest of this code at the same time
     // Based on https://stackoverflow.com/a/5429695/531762
-    std::unique_lock<std::mutex> lock(_reloadCellsMutex);
+    std::unique_lock<std::mutex> lock(reloadCellsMutex);
 
     // The following code will run only if there is not another thread currently running it
     CellNameLoader cellNameLoader;

apps/openmw/mwgui/journalwindow.cpp

@@ -83,16 +83,16 @@ namespace
                 setVisible (visible);
         }
 
-        void adviseButtonClick (char const * name, void (JournalWindowImpl::*Handler) (MyGUI::Widget* _sender))
+        void adviseButtonClick (char const * name, void (JournalWindowImpl::*handler)(MyGUI::Widget*))
         {
             getWidget <MyGUI::Widget> (name) ->
-                eventMouseButtonClick += newDelegate(this, Handler);
+                eventMouseButtonClick += newDelegate(this, handler);
         }
 
-        void adviseKeyPress (char const * name, void (JournalWindowImpl::*Handler) (MyGUI::Widget* _sender, MyGUI::KeyCode key, MyGUI::Char character))
+        void adviseKeyPress (char const * name, void (JournalWindowImpl::*handler)(MyGUI::Widget*, MyGUI::KeyCode, MyGUI::Char))
         {
             getWidget <MyGUI::Widget> (name) ->
-                eventKeyButtonPressed += newDelegate(this, Handler);
+                eventKeyButtonPressed += newDelegate(this, handler);
         }
 
         MWGui::BookPage* getPage (char const * name)