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

click the new UI elements and they worked. edited a document with signatures, noted warning UI, edited anyway, noted warning UI correctly disappeared on new edit. also verified a single signature had the correct translation