Add a feature to save/restore compare options to/from a project file. (#915)

Add a feature to save/restore compare options to/from a project file. (#915)

Also, change the behavior of the "Options..." popup menu in the Select Files or Folders dialog.
- Even if the values in the popup menu are changed, it is not saved in the WinMerge option at that time.
- The values in the popup menu are saved in the WinMerge options when the "Compare" button is clicked.
- The "Include Subfolders" item in the popup menu is deleted.