Add std::set support

[leemaguire]

Adds support for std::set in object models.

    struct SetTypesObject {
        primary_key<int64_t> _id;
        std::set<int64_t> set_int_col;
        std::set<double> set_double_col;
        std::set<bool> set_bool_col;
        std::set<std::string> set_str_col;
        std::set<realm::uuid> set_uuid_col;
        std::set<realm::object_id> set_object_id_col;
        std::set<std::vector<std::uint8_t>> set_binary_col;
        std::set<std::chrono::time_point<std::chrono::system_clock>> set_date_col;
        std::set<realm::mixed> set_mixed_col;
        std::set<AllTypesObjectLink*> set_obj_col;
    };

    REALM_SCHEMA(AllTypesObject,
                 _id, set_int_col, set_double_col, set_bool_col, set_str_col, set_uuid_col, set_object_id_col, set_binary_col,
                 set_date_col, set_mixed_col, set_obj_coll)