Continuous improvement of metadata collected - online form

[BenjMy]

During a new contribution submission, the online form, yet in its beta version, should:

• [ ] propose a questionnaire to identify user requirements and ensure that CAGS addresses the existing and emerging needs of the geophysical research community.
• [x] propose a link to open an issue when missing entries

Already identified missing entries:

• [ ] add multiple contributors/role, see postdam gfz metadata editor
• [ ] add multiple entries for lat/long coordinates when fields are distributed over several places.

[sagitta1618]

In input_form.html, for some fields (like instrument, method, ...), it is possible to add a new category straight in the form. This is made possible by the jQuery select plugin. If fields are missing, user can provide additinal data in the 'comment' section at the end of the form or open an issue on github.