New static-template group

[folbricht]

Related to #366

Introduces a new group static-template which works exactly like static-responder but instead of plain strings uses templates that are processed at query-time allowing responses to be based on data in the query such as the question, type, id, or class. For example:

[groups.static]
type   = "static-template"
answer = [
    '{{ .Question }} IN {{ .QuestionType }} {{ trimSuffix .Question ".rebind."}}'
]