Bug/5739 fix multipart put problem 2

This pull request addresses the following issues:

* Avoid the multipart PUT bigcouch bug by using a new HTTP resource for each multipart PUT request. Also remove old workaround of closing connections everytime and let the python-couchdb module reuse connections for every non-mutipart request.
* Get rid of client-side sync state because that is not necessary and makes things more complicated than they need to be. That is replaced by a sync_id which is created for every new sync attempt in the client.
* Fix a bug where we have to reset the synchronizer state if we want to reuse it multiple times.
* Move the soledad syncing log to a better place, inside SQLCipherDatabase class.
* Includes the following old pull request, because webapp has implemented it in this cycle: https://github.com/leapcode/soledad/pull/57/files