R1:5242fb057251

Add a "documents I've signed" view to Legalpad

Summary:
Ref T3116. Allow documents to be queried for ones the viewer has signed, and make this the default view.

This also relaxes the versioning stuff a little bit, and stops invalidating signatures on older versions of documents. While I think we should do that eventually, it should be more explicit and have better coordination in the UI. For now, we'll track and show older signatures, but not invalidate them.

I imagine eventually differentiating between…