In tree view, add an internal link to the file diff in the page

[xavier-rdo]

Pre-requisite : fix #7 first (as it has many structural consequences).

Foreach file diff in the Github page, an anchor exists :

<a name="diff-194d67220562af5133cad352f6ca7ede"></a>

Add this data in the object domain/model.js/GitFile and implement it in the tree view (link to the file diff in the current page).

Nota: content.js must be updated to retrieve that information from the DOM and GithubParser must also be updated.