Make sure bookmarks survive a document reload

While reloading a text document, the bookmarks got lost since their
associated QTextBlocks were deleted.

This patch makes sure that before reloading, the bookmarks are removed
non-persistently in the same way as when closing a document, and that
they are restored after the document was reloaded.

Currently, no effort is made to update the location of the bookmarks
based on the way the file changed.

Task-number: QTCREATORBUG-1281
Reviewed-by: dt

src/plugins/resourceeditor/resourceeditorw.cpp

@@ -203,7 +203,9 @@ void ResourceEditorFile::reload(ReloadFlag flag, ChangeType type)
     if (type == TypePermissions) {
         emit changed();
     } else {
-        m_parent->open(m_parent->m_resourceEditor->fileName());
+        emit aboutToReload();
+        if (m_parent->open(m_parent->m_resourceEditor->fileName()))
+            emit reloaded();
     }
 }