DBFlute Engine: option to make AppCDef simple determination method e.g. isXxx()

[jflute]

This is user feedback. (thanks)

Improvement image:

if (result.memberStatusCode == XxxCDef.MemberStatus.Formalized) {
}
↓
if (result.memberStatusCode.isFormalized()) {
}

Especially for RemoteApi.

First, I will support it as option and only application classification. (e.g. DB classification has Entity, CB methods)

The possibility of confliction with is[Group]() is allowed.