Use GetFileName() when it makes sense to.

This ensures that:
 - the real filename of the file will be used when playing a RARed media file,
 - stream URLs will be correctly stripped (e.g. "http://server/mystream" will be stripped to "mystream").
OSD: The bounding rectangle was too small if "&" appeared in the text.
OSD: Sanitize the positioning of the text and its frame.

Displaying an identical message on top left or top right resulted in different frame size. Also improve the behavior when the text is too big to be displayed entirely.
Update translations from Transifex:

 - Galician
 - Japanese
 - Romanian
 - Vietnamese
Language menu: Ensure "Language" always appears in English in menu entry.

If "Language" doesn't appear in the translated string, "(Language)" will be appended automatically.
Language menu: Use submenus to group language names starting with the same character.
Update translations from Transifex:

 - Greek.