Performance improvements

On localhost it is unnoticeable, however on a remote server we can benefit of loading the breadcrumbs/file path menu, later than the file contents. 
Also loading the file contents asynchronously and switching to the newly selected file (even though the content is still not loaded) I think looks better than "freezing" for a part of the second. 
It looks at some point the request "get?file=..."  was asynchronous, but was changed to synchronous...