Added previous changelog
Relaxed requirements of FilePreviewHandler::ClearAndSetDataToWidget
Created ImagePreviewHandler
ImagePreviewHandler goes on operation.
Implemented TextPreviewHandler
Context menu for BMViewDlg attached files.
In BMViewDlg clicking files will preview them.
Try not to preview BMView files on right-click
I failed at previous commit

We have to handle the right-click event for the purpose of that, but we
are using customContextMenuRequested. Reverted most of the changes and
also removed autoPreviewFileOnSelection.
So af_preview is not needed, we always preview.
Set override cursor on previewing the files.

But this doesn't work when WebKit is actually rendering the things.
We no more clear the files selection in BMViewDlg.

Because we don't show any menu for its "empty" area.
Introduced FileViewManager::ShowProperties, but still not implemented