* pushsync: reuse overlapping logic, improve instrumentation, don't bail on invalid receipt

- add API endpoint for listing tags from store
- rename 'swarm-tag-uid' header to 'swarm-tag'
- rename field 'stored' to 'processed'
- estimate total number of chunks during upload

Fixes #1188

* feeds: 
   - generic feed support building on single owner chunks
   - subpackages for epochs and sequence based indexing scheme implementing timestamped feeds 
   - Lookup interface with both sequential and concurrent lookup algorithms 
   - Updater interface 
Co-authored-by: zelig <viktor.tron@gmail.com>