Allow widget configuration via options dict and data attribute

[sweh]

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

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Currently some configuration is supplied via the options dict when creating an instance of gocept.jsform, other options are read from the template via data-attributes.

It would be nice if all widget specific configuration can be done both ways, thus gocept.jsform has to check the options dict and the data-attributes of the template. The documentation should tell that both ways are supported and which is preferred if both are given.

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• Bitbucket: https://bitbucket.org/gocept/gocept.jsform/issue/22