Docs: Removed file comments and added missing code documentation

Please note that file comments had no purpose in nearly all cases and just added visual clutter. The two files that had meaningful file comments had their comments moved into the corresponding classes. There are still hundreds of file comments left in other files that will be removed over time.

Also cleaned up some random stuff along the way:
- relative paths to public headers within the same module are no longer necessary (automatically discovered by UBT now)
- header guards are deprecated, use #pragma once instead (all compilers support it now)
- space between multiple template brackets is no longer required (all compilers support >> now)
- NULL to nullptr, OVERRIDE to override
- spelling errors, whitespace, line breaks

[CL 2104067 by Max Preussner in Main branch]

Engine/Source/Programs/UnrealFrontend/Private/UnrealFrontendMain.cpp

@@ -1,9 +1,5 @@
 // Copyright 1998-2014 Epic Games, Inc. All Rights Reserved.
 
-/*=============================================================================
-	UnrealFrontendMain.cpp: Implements the UnrealFrontend application's main loop.
-=============================================================================*/
-
 #include "UnrealFrontendMain.h"
 
 #include "RequiredProgramMainCPPInclude.h"
@@ -21,6 +17,7 @@ IMPLEMENT_APPLICATION(UnrealFrontend, "UnrealFrontend");
 
 #define IDEAL_FRAMERATE 60;
 
+
 namespace WorkspaceMenu
 {
 	TSharedRef<FWorkspaceItem> DeveloperTools = FWorkspaceItem::NewGroup( NSLOCTEXT("UnrealFrontend", "DeveloperToolsMenu", "Developer Tools") );