Add libraryPaths array to Project element (.qmlproject format)

Will be passed to qmlviewer with the "-L" option. Storing this in
the .qmlproject file format itself (and not in the .user file) is useful
in case the libraries are relative/part of the checkout that is shared
between users/computers.

src/plugins/qmlprojectmanager/fileformat/qmlprojectitem.h

@@ -23,6 +23,7 @@ class QmlProjectItem : public QObject {
 
     Q_PROPERTY(QmlList<QmlProjectManager::QmlProjectContentItem*> *content READ content DESIGNABLE false)
     Q_PROPERTY(QString sourceDirectory READ sourceDirectory NOTIFY sourceDirectoryChanged)
+    Q_PROPERTY(QStringList libraryPaths READ libraryPaths WRITE setLibraryPaths NOTIFY libraryPathsChanged)
 
     Q_CLASSINFO("DefaultProperty", "content");
 
@@ -35,11 +36,15 @@ public:
     QString sourceDirectory() const;
     void setSourceDirectory(const QString &directoryPath);
 
+    QStringList libraryPaths() const;
+    void setLibraryPaths(const QStringList &paths);
+
     QStringList files() const;
 
 signals:
     void qmlFilesChanged();
     void sourceDirectoryChanged();
+    void libraryPathsChanged();
 
 protected:
     QmlProjectItemPrivate *d_ptr;