Implement BlockMap
Populate BlockMap
Implement block fetcher (fixes #781, fixes #3)
Fix tests
Track total block counts, count copier blocks

Will eventually allow us to track progress per file
Add fetcher tests
Delete files and directories after pulling
Merge branch 'pr/830'

* pr/830:
  Delete files and directories after pulling
  Add fetcher tests
  Track total block counts, count copier blocks
  Fix tests
  Implement block fetcher (fixes #781, fixes #3)
  Populate BlockMap
  Implement BlockMap
Don't log inscrutable 'recovered: leveldb: not found' to web GUI