Overhaul plat_get_string()

Now takes constants with human-readable names instead of
Win32 string table IDs, language.h is no longer needed

ui_msgbox*() no longer accepts string IDs as arguments directly,
plat_get_string() must be explicitly called to retrieve the string

src/disk/hdd.c

@@ -53,7 +53,7 @@ hdd_string_to_bus(char *str, int cdrom)
     if (!strcmp(str, "mfm") || !strcmp(str, "rll")) {
         if (cdrom) {
 no_cdrom:
-            ui_msgbox_header(MBX_ERROR, (wchar_t *) IDS_2131, (wchar_t *) IDS_4099);
+            ui_msgbox_header(MBX_ERROR, plat_get_string(STRING_INVALID_CONFIG), plat_get_string(STRING_NO_ST506_ESDI_CDROM));
             return 0;
         }