Replace Save dialog with two commands: «Save as» and «Export as». Supporting features:

* save file names are auto-suggested based on URL and title;
* export files are saved with «.export.html» extension by default;
* auto-export feature is added (it allows doing the export in addition to save on Save as command);
* folders with images/css/other resources are named automatically;
* there is an option to make all links absolute (so that page will display as before after saving);
* there is an option to add <base> html tag to page as an alternative for making links absolute (sometimes it is important to preserve relative links);
Remove unneeded option from defaults; make saving to unmodified HTML default