renamed ICU chain functions to the following names relation the operation

renamed ICU chain functions to the following names relation the operation
to the actually processed token

int          icu_chain_token_number(struct icu_chain * chain);
const char * icu_chain_token_display(struct icu_chain * chain);
const char * icu_chain_token_norm(struct icu_chain * chain);
const char * icu_chain_token_sortkey(struct icu_chain * chain);