Write a method called isAllVowels that returns whether a string consists entirely of vowels (a, e, i, o, or u, case-insensitively). If and only if every character of the string is a vowel, your method should return true . For example, the call isAllVowels("eIEiO") returns true and isAllVowels("oink") returns false . You should return true if passed the empty string, since it does not contain any nonvowel characters.