* manifest: removed explicit refresh
Instead, content manager is exposing a revision counter that changes
on each mutation or index change. Manifest manager will be invalidated
whenever this is encountered.
* server: refactored initialization API
* server: added unit tests for repository server APIs (HTTP and REST)
* server: ensure we don't upload contents that already exist
This saves bandwidth, since the client can compute hash locally
and ask the server whether the object exists before starting the upload.
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