Starred documents tab

Because client.starredTab is meant to be the delegate of Document(json, delegate) and I found it dirty to access it via `client.tabs[1]`.

The thing is client.timelineTab is still useless, and client.tabs is used by a loop in the view app.html. Should we kick client.timelineTab ?

I'm also gonna make a client.providerTab to simplify conditions in app.html, actually you can find things like `if activeTab().name ===  "Providers"` which is worst than tabs[2] :-1: