Copy canonical/shortlink/shorturl as url if it exist in header.

Signed-off-by: Rex Tsai <chihchun@kalug.linux.org.tw>
declares canonical variable.

Signed-off-by: Rex Tsai <chihchun@kalug.linux.org.tw>
Support canonical/shortlink/shorturl for menuContextSelection.

Signed-off-by: Rex Tsai <chihchun@kalug.linux.org.tw>
Merge pull request #2 from chihchun/canonical

Copy canonical/shortlink/shorturl as url if it exist in header.