Change File System pane to a forest of trees

It shows the file system as a tree, where the user can change the root
directory of the view. Currently there are "Computer" (the default), and
all project directories.
If synchronization with the current editor is enabled, the view
automatically switches to the best fitting root directory.

Task-number: QTCREATORBUG-8305
Change-Id: Ic265eb49b1e8e0fd8cdeeb4fb1c64b8631f32e21
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

src/plugins/projectexplorer/session.cpp

@@ -30,6 +30,7 @@
 #include "kit.h"
 #include "buildconfiguration.h"
 #include "deployconfiguration.h"
+#include "foldernavigationwidget.h"
 #include "projectexplorer.h"
 #include "projectnodes.h"
 #include "editorconfiguration.h"
@@ -385,6 +386,8 @@ void SessionManager::addProject(Project *pro)
             m_instance, [pro]() { m_instance->projectDisplayNameChanged(pro); });
 
     emit m_instance->projectAdded(pro);
+    FolderNavigationWidgetFactory::addRootDirectory(pro->displayName(),
+                                                    pro->projectFilePath().parentDir());
     configureEditors(pro);
     connect(pro, &Project::fileListChanged, [pro](){ configureEditors(pro); });
 }
@@ -739,6 +742,7 @@ void SessionManager::removeProjects(QList<Project *> remove)
                    m_instance, &SessionManager::clearProjectFileCache);
         d->m_projectFileCache.remove(pro);
         emit m_instance->projectRemoved(pro);
+        FolderNavigationWidgetFactory::removeRootDirectory(pro->projectFilePath().parentDir());
         delete pro;
     }