Copy form, question and option

[anehx]

See projectcaluma/caluma#255 for backend implementation.

A few things to note:

• A copy of a form will reference the same questions as previous forms
• Copy of questions will reference the same options as previous questions.

Both of this is important that jexl expression are still valid in a new form context.

After a copy has been made user interface has to guide user so it notices when a question resp. option is updated on all form copies or whether the question is only added to current form.

This is especially true for options as user interface looks at them as not global but in the backend they are because of keeping jexl expression valid and multi language support.