Make Search ignore accents for address book summary searches

Make Search ignore accents for address book summary searches

	** Partial fix for bug #343505

        * libedataserver/e-data-server-util.h: (e_util_utf8_remove_accents):
        * libedataserver/e-data-server-util.c: (e_util_utf8_remove_accents):
        Helper function to remove accents from a UTF-8 string.

        * libedata-book/e-book-backend-summary.c: (contains_helper),
        (func_contains), (is_helper), (endswith_helper), (beginswith_helper):
        * libedata-book/e-book-backend-sexp.c: (chars_to_unistring_lowercase),
        (is_helper), (endswith_helper), (beginswith_helper), (exists_helper),
        (func_exists): Compare texts without accents.