Flat and themeable side bar icons

This patch adds flat side bar icons according to
http://blog.qt.io/blog/author/didesous/

The flat icons are supposed to be opt-in, via the theme flag
"FlatSideBarIcons=true". It is false by default for the default
theme for now.

Change-Id: I1cbe69d4e138d5d23c0172a374933ac7a4ce8a5b
Reviewed-by: Alessandro Portale <alessandro.portale@theqtcompany.com>

src/plugins/help/help.qrc

@@ -7,6 +7,8 @@
         <file>images/category_help.png</file>
         <file>images/mode_help.png</file>
         <file>images/mode_help@2x.png</file>
+        <file>images/mode_help_mask.png</file>
+        <file>images/mode_help_mask@2x.png</file>
     </qresource>
     <qresource prefix="/trolltech/assistant" >
         <file>images/mac/addtab.png</file>

src/plugins/help/helpmode.cpp

@@ -30,6 +30,7 @@
 
 #include "helpmode.h"
 #include "helpconstants.h"
+#include "helpicons.h"
 
 #include <QCoreApplication>
 
@@ -41,7 +42,8 @@ HelpMode::HelpMode(QObject *parent)
 {
     setObjectName(QLatin1String("HelpMode"));
     setContext(Core::Context(Constants::C_MODE_HELP));
-    setIcon(QIcon(QLatin1String(":/help/images/mode_help.png")));
+    setIcon(Utils::Icon::modeIcon(Icons::MODE_HELP_CLASSIC,
+                                  Icons::MODE_HELP_FLAT, Icons::MODE_HELP_FLAT_ACTIVE));
     setDisplayName(QCoreApplication::translate("Help::Internal::HelpMode", "Help"));
     setPriority(Constants::P_MODE_HELP);
     setId(Constants::ID_MODE_HELP);