Use consistent encoding names in settings and menu

[Akaizoku]

Issue

The name of the character encodings available in settings does not match the name of the encoding available from the menu (View/Navigate > Encoding).

Encoding	Settings	Menu
ASCII	us-ascii	ASCII
Windows-1252	Windows-1252	Windows-1252
ISO-8859-1	iso-8859-1	ISO-8859-1
UTF-8	utf-8	UTF8
UTF-16	utf-16	Unicode

[Hirogen]

Should be fixed with #227