code refactor and fixes

- moved and reorganized scripts into separate folder
- added scripts for creating / unmounting loopback devices to be used as user home
- common base class for dynamodb tables
- jbox.user can now override only part of the entries of nested sections
- corrected accounting table code
- corrected websockets cors issue
- added SIUnits to packages installed (required for oft used sample notebooks)
better mount script
Merge pull request #85 from tanmaykm/tanmaykm

code refactor and fixes