Move RewindDumper control into master

* Master: Create `rewind_dr` object for managing dump and restore
* Dumper: Add RewindDumpRestore manager class
* Rewind: Remove direct connection to dumper
* Update tests
Rewind Dump/Restore work; Rebuild `dumpBuffer`

* MasterMode: Call `loadRewinds` except when running a handoff
* Master: emit `new_stream` when a stream is registered
* RewindBuffer: Restructure `dumpBuffer` to return a readable stream,
  rather than take a writable one
* RewindDumpRestore: Account for new streams and ones that go away
* AdminRouter: Add GET and DELETE endpoints for stream rewind buffers
* Update tests