Predefined title sequence filenames are now treated as "reserved".
Custom title sequences cannot use reserved names and an error will
appear if the user tries.
Duplicating predefined title sequence now uses default text of
predefined sequence's proper name instead of filename.
Renamed `WIDX_TITLE_EDITOR_RENAME_SAVE_BUTTON` to
`WIDX_TITLE_EDITOR_RENAME_BUTTON` to follow formatting of other preset
button ids.
Added string id 6154, `STR_ERROR_RESERVED_NAME`, "Name is reserved".