Bug 860910 - Patch (v6) NFC System app integration: activies and messages, and airplane mode.

- Fix review comments, and some nits.
- Fix contacts, now forwards via activity as-is to import vcard activity in contacts.

Other comments:
- the "handle<TYPE>" functions are needed (unless there's a better way), especially when a type has to be manipulated before sending an activity.
- Contacts seems to have a working import "text/vcard" from a blob, we use that instead of the old imcomplete vcard parser implementation, and pass the parsing duties to the contacts app, where it belongs. There's many types of vcards, so we might need to revisit this.