Reworked document opening and saving.

Without an existing metafile, try to open any document as utf8 first,
then latin1. Do not use suffixes anymore.

When saving a document, try to save it as latin1 if possible. If not
possible, save it as utf8. Same as Guiguts.
Display the encoding used to save the file in the title bar, alongside the file name.
TODO: However that should disappear as soon as the document is changed.