Doc: Update Tweet Search Demo to use Twitter Search API v1.1

Twitter REST API v1 is no longer supported. This change updates the
Tweet Search Demo to use the new version (v1.1). Specifically,
    - Use of OAuth tokens (authentication required in v1.1)
    - JSON parsing for results instead of XML
    - Use of url/hashtag/username entities returned in search results

Also, update the documentation to discuss authentication and
registering the application to dev.twitter.com.

Task-number: QTBUG-31745
Change-Id: I00cd7b07f065babb03483daabe8df22f22995c29
Reviewed-by: Alan Alpert <aalpert@blackberry.com>