Parse the user id (nsid) and photo/set id from the Flickr page URL

Background
Current the flickr field asks for 3 different user inputs:
Item Type
Id
and User Id.

Motivation

• All of this information can be supplied from a simplified, unique identifier - URL
• Even when I know the values I want in the fields, it's cumbersome to copy and paste them from the URL, or god forbid I have to go search for my nsid.
• The flickr URL contains enough information for flickr API to retrieve all the necessary info for the asset without any additional input from the end user
• Regardless of whether these 3 fields are stored in the database, exposing the user to the underlying schema is confusing.

Solution
Only collect the asset URL from the user (set URL or photo URL), parse the photo or set id from it.

In this patch

• in flickr.inc: added flickr_get_info_by_url(). Given the URL to a flickr asset (set or photo), return info about that asset.
• in flickrfield.module: Update flickrfield_process() to provide a single text field for user input.
• in flickrfield.module: Add flickrfield_field() with validate and presave operations to populate the existing columns

Note that flickrfield schema is not changed by this patch.