Add save button to form that waits for server side validation before send

[sweh]

Originally reported by: Florian Pilz (Bitbucket: florianpilz, GitHub: florianpilz)

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When using a form with a save button, you currently have to manually check that all fields were successfully saved before submitting the form. It would be great if gocept.jsform provides a custom save button, that by itself calls save_remaining and waits for successful responses.

There already is some support build into gocept.jsform to do so, but the integration must be done manually in each project. Very cumbersome, since this behaviour is needed in almost any form. (When typing into an input field and clicking save before it lost focus you need to make sure the filed was saved before performing the submit.)

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• Bitbucket: https://bitbucket.org/gocept/gocept.jsform/issue/26