move/delete directories (Fixes #234)

Pulled out calls to the mongo driver into a MongoWrapper trait which
puts everything into Task.

Additional tests.

Switch to mongolabs for integration tests.
update README; respond to comments

Moved integration test to the common fs package.

Couple of additional tests for API operations on dirs.
Merge pull request #246 from mossprescott/234-move-dirs

move/delete directories (Fixes #234)