Added twig filter to edit the source url

Added a twig filter to turn urls like `git@bitbucket.org:Comapny/repo.git` into `http://bitbucket.org/Comapny/repo.git`

Without this fix, the link to any release would be `http://satis-domain.com/git@bitbucket.org:Comapny/repo.git`. 
Thank you @kaiwa but that does not work with Bitbucket private repos. I need to use ssh and a ssh key, satis will ask me for authentication otherwise...

``` bash
$ php bin/satis build satis.json web/
Scanning packages
    Authentication required (api.bitbucket.org):                     
      Username: 
```