Remove the use of "signatures"

In trunk we can get the md5 of existing attachments in a designdoc request, even without that the signatures should be a local cache file so we dont have the problem where a couchapp is update without the signatures being updated, which will then cause any changes the user makes to have no effect until signatures is deleted.

Start by locating the code that handles signatures and the designdoc request in this Couchapp management tool. Trace how attachment MD5 values and signature data are stored or read. Done means signature state is local and updating a Couchapp cannot leave user changes ineffective because of stale signatures.

Written by the indexing model from the issue text.