aggregate fixity
Cleaned up unused imports
Merge branch 'master' into agg-fixity

* master:
  Cleaned up unused imports
Small improvement to LowLevelStorageService
Small improvement to LowLevelStorageService
Merge branch 'master' of github.com:futures/fcrepo4
More improvements to the implementation of LowLevelStorageService
Merge branch 'master' of https://github.com/futures/fcrepo4