Infer table schema when a suitable file is selected

[amercader]

As discussed in #65, When a user selects a suitable file, fire a background HTTP request to the action created in #76 to get an inferred table schema.

• Re-use or adapt code from Schema editor integration #25 that listen to changes in the Upload button,
• Check if the extension is one of the ones supported.
• If so read the whole file or a sample if it's bigger than X and use the ckan JS client to call the action with this data and the format
• If we get a response and there are no errors, we store the result in the schema_json field (let's get this down first and we'll render the editor component later)
• If there are errors display them

[amercader]

Closing as no longer relevant