Reintroduced a way to edit project dependencies

Dependencies between projects can now be edited in the Projects mode.
You can simply check for each project the projects that it depends on,
and they will be built first. A message box pops up when you try to
create a circular dependency.

Could use some testing.

src/plugins/qt4projectmanager/qt4projectmanager.cpp

@@ -74,7 +74,12 @@ using ProjectExplorer::ResourceType;
 using ProjectExplorer::UnknownFileType;
 
 // Known file types of a Qt 4 project
-static const char* qt4FileTypes[] = {"CppHeaderFiles", "CppSourceFiles", "Qt4FormFiles", "Qt4ResourceFiles" };
+static const char* qt4FileTypes[] = {
+    "CppHeaderFiles",
+    "CppSourceFiles",
+    "Qt4FormFiles",
+    "Qt4ResourceFiles"
+};
 
 Qt4Manager::Qt4Manager(Qt4ProjectManagerPlugin *plugin, Core::ICore *core) :
     m_mimeType(QLatin1String(Qt4ProjectManager::Constants::PROFILE_MIMETYPE)),