model sorting in list view is very heavy, so do not response item added in enumeration process will resolve this problem.

for old frameworks, the thumbnail is actually a whole image, and thumbnailing thread can not be cancel.
so that it has serious flaws in memory usage.

first what i do is to let the image scaled into a smaller size if it is too big. it will ensure that
when all thumbnail job finished, the memory usage will not become so scaring.

second i do is to use a thumbnail job bounded with a directory item parent, when item deleted it should
not do a thumbnail. it will actually limit the Instantaneous peak of memory usage.

the main idea is:
1. replace QtConcurrent::run() with a QRunnable, limit thread count with QThreadPool instance.
2. use QObject parent mechanism control the job's running.

DesktopWindow: 1. refactor the bg painting process. 2. improve the process responsing screen geometry changed.

Note that the old screen-desktopwin-view frameworks is FULL of HOLES. I have to refactor that so it could be simple and correct.

right click will handle selection correctly in different cases.

Fix crash issue when use Alt + Enter without any selections

FileOperation: rollbacking handling file item correctly. fix issue#89.

When some times we refresh model too frequently, the items will could not be queried correctly.
so limit the refresh frequency will help us reduce the risk for query missing.

when change file content and close file(#69). FileItem::onChildAddedwas called. m_model may already have child, but child info may be changeed. So child info need to update.

Copy same file to desktop twice, it should call FileOperationErrorDialog to show error info. but when FileOperationProgressWizard showed, it cause previous dialog flashed once.
Even though FileOperationErrorDialog only show once but it looks like this dialog have showed twice. We should use WindowStaysOnTopHint to make sure this dialog show on top to avoid this problem.

When the screen geometry changed, window will be updated, but view item might be relayout in error places.
Refreshing the view will let an item restore its previous position in the view.

Remove useless fiels; update copyright;add keywords to desktop and change the install path; remove Breaks/Replaces; fix spelling errors; update the translation; add libpeony2.symbols

1. advance-search-bar：add setdefaultpath function.
2. use current path as default search path.