Adapt to new tomboy-library

- As tomboy-library steers towards PCL, there is no File.* anymore so
  the SyncManifest.Read/Write only operates on streams
- DevDefined.OAuth is no longer needed and dropped as dependency
- DiskStorage.SetPath is deprecated (path should go into constructor)
Merge pull request #14 from Dynalon/master

Adapt to new tomboy-library