[Firefox] Show moreFields when editing a feature

[Binnette]

Hi @DoFabien, I wanted to show the tags included in the property "moreFields" when when edit a feature.

I succeed to do so. But I really think my way to do it is VERY ugly. I don't know Osm Go! code base enough to propose a better solution.

Can you please implements your own solution ?

Note: that I also implement a mechanism to automatically set the preset type to text if is type is list, select or combo and no options is provided.