R1:c40420eb7465

Legalpad - a few rough edges smoothed...

Summary:
does a few smallish things... Ref T3116

- adds an action to "sign document", thus improving visiblity of this feature from 0 to some value more than 0
- adds a crumb on the edit page to get back to the view page
- warns the user on the edit page IFF signatures exist for the current version that their edits could invalidate those signatures
- adds a "needSignatures" option to the Document Query class

Test Plan: click the new UI elements and they…