code: Refactor code browser and code history.

* Merge CodeApp.getURL and CodeApp.getSvnURL.
* In views for Code Browser and Code History, when getting a url to
clone a repository, use CodeApp.getURL instead of an argument passed as
the url.
code: Fix an inappropriate message.

"CLONE THIS REPOSITORY" is not proper message for SVN repository. Use
more neutral message, "REPOSITORY URL."