Render Schema editor

[amercader]

After we successfully get a Table Schema (see #77) display a UI to the user to tweak it.

As per @roll comment on #65 we will have to make do with the old component used in #25, although there are some things that need to be fixed (like the buttons).

We can take this opportunity to rethink the whole UI of the resource form, perhaps bringing the Schema related fields closer to the File ones.
One thing I think could work well is to display a table with a sample of the first 5-10 rows of the data, including the inferred field type in the headers, and a separate Customize or Edit button that opens a popup with the Schema Editor. Opening the editor directly after selecting a file might be confusing as users are more used to the table view than the field list view of the editor.

Let's discuss