Make the welcome screen into plugins.

This removes the all hard dependencies to and from welcome screen,
except the one to the core plugin. More in detail:

- Add IWelcomePage to add a tab to the welcome screen
- Move tabs in the modules where they belong
- Enables QHelpManager to open help fullscreen and contextually
- "Getting Started" moves to Qt4ProjectManager
- Projects & Sessions (aka "Develop") moves to ProjectExplorer
- "Community" remains in the welcome plugin for simplicity

src/plugins/welcome/welcomeplugin.cpp

@@ -31,6 +31,8 @@
 
 #include "welcomemode.h"
 
+#include "communitywelcomepage.h"
+
 #include <coreplugin/actionmanager/actionmanager.h>
 #include <coreplugin/basemode.h>
 #include <coreplugin/coreconstants.h>
@@ -45,11 +47,10 @@
 #include <QtGui/QMessageBox>
 #include <QtGui/QPushButton>
 
-using namespace Welcome;
-
+using namespace Welcome::Internal;
 
 WelcomePlugin::WelcomePlugin()
-  : m_welcomeMode(0)
+  : m_welcomeMode(0), m_communityWelcomePage(0)
 {
 }
 
@@ -59,6 +60,10 @@ WelcomePlugin::~WelcomePlugin()
         removeObject(m_welcomeMode);
         delete m_welcomeMode;
     }
+    if (m_communityWelcomePage) {
+        removeObject(m_communityWelcomePage);
+        delete m_communityWelcomePage;
+    }
 }
 
 /*! Initializes the plugin. Returns true on success.
@@ -72,6 +77,9 @@ bool WelcomePlugin::initialize(const QStringList &arguments, QString *error_mess
     Q_UNUSED(arguments)
     Q_UNUSED(error_message)
 
+    m_communityWelcomePage = new Internal::CommunityWelcomePage;
+    addObject(m_communityWelcomePage);
+
     m_welcomeMode = new WelcomeMode;
     addObject(m_welcomeMode);
 
@@ -91,6 +99,7 @@ bool WelcomePlugin::initialize(const QStringList &arguments, QString *error_mess
 */
 void WelcomePlugin::extensionsInitialized()
 {
+    m_welcomeMode->initPlugins();
     Core::ModeManager::instance()->activateMode(m_welcomeMode->uniqueModeName());
 }