qmljs: improve handling of qml dialects

Language::Enum -> QmlDialect
 * class instead of enum
 * moved Language specific operations to it (from Document)
 * nicer handling
QStringList -> PathsAndLanguages
 * store language along with path, to perform a correct scan and improve
   path handling

Change-Id: If69d35c63cfeb48aa670b51870916cd0c40f1916
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>

src/plugins/qmlprojectmanager/qmlproject.cpp

@@ -201,7 +201,9 @@ void QmlProject::refresh(RefreshOptions options)
 
     QmlJS::ModelManagerInterface::ProjectInfo projectInfo =
             modelManager()->defaultProjectInfoForProject(this);
-    projectInfo.importPaths = customImportPaths();
+    foreach (const QString &searchPath, customImportPaths())
+        projectInfo.importPaths.maybeInsert(Utils::FileName::fromString(searchPath),
+                                            QmlJS::Dialect::Qml);
 
     modelManager()->updateProjectInfo(projectInfo, this);
 }