Implement a CSV import page for admins

[jrobbins]

Sometimes we want to do bulk edits using data from spreadsheets. E.g., we would like to import the web feature IDs for each chromestatus entry linked in this spreadsheet: http://bit.ly/webdxuc.

I am thinking of:

• A form where the admin can upload a CSV file
• Some <select> form fields where they can choose the column that holds the chromestatus entry URL, and the column that holds the web feature ID.
• A button to preview that the changes would be.
• After the preview is viewed, there would be a button to make the changes.

I am thinking that the changes would be made via our existing feature_api and they would cause all the normal permission checks and notification emails individually rather than have a new bulk edit API.

Later we might generalize the form to update some other chromestatus fields.

[jrobbins]

This is live now and has been used.
I didn't implement the but the naming convention for the needed columns seems good enough.