Remove trailing whitespaces

Many tools strip trailing whitespaces by default, so after editing a file with
whitespace errors we end up with a bunch of unrelated hunks that need to be
reverted locally.

This could be fixed by configuring each tool to not do this (at least for the
barrier repo), or, simpler, we just sed the problem away and make barrier
whitespace-compliant.

sed commands run:
    sed -i 's/[ \t]\+$//' **/*.(cpp|h) **/*CMakeLists.txt

Verified with git diff --ignore-space-change, this shows the empty diff.

src/lib/platform/MSWindowsScreen.h

@@ -3,11 +3,11 @@
  * Copyright (C) 2018 Debauchee Open Source Group
  * Copyright (C) 2012-2016 Symless Ltd.
  * Copyright (C) 2002 Chris Schoeneman
- * 
+ *
  * This package is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License
  * found in the file LICENSE that should have accompanied this file.
- * 
+ *
  * This package is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
@@ -212,12 +212,12 @@ private: // HACK
 
     // our window proc
     static LRESULT CALLBACK wndProc(HWND, UINT, WPARAM, LPARAM);
-    
+
     // save last position of mouse to compute next delta movement
     void saveMousePosition(SInt32 x, SInt32 y);
 
     // check if it is a modifier key repeating message
-    bool                isModifierRepeat(KeyModifierMask oldState, 
+    bool                isModifierRepeat(KeyModifierMask oldState,
                             KeyModifierMask state, WPARAM wParam) const;
 
     // send drag info and data back to server
@@ -324,12 +324,12 @@ private:
     bool                m_gotOldMouseKeys;
     MOUSEKEYS            m_mouseKeys;
     MOUSEKEYS            m_oldMouseKeys;
-    
+
     MSWindowsHook        m_hook;
 
     static MSWindowsScreen*
                         s_screen;
-    
+
     IEventQueue*        m_events;
 
     std::string                m_desktopPath;