Exposed postgresql from container to host to be able
to browse database easily for debugging purposes.

- added presenting subnet utilization and subnet stats in subnets and
  shared-networks pages in UI
- added ui component 'subnet-bar' for preseting subnet utilization
  with tooltip that shows details info about stats
- added subnet details while returnin shared-networks in ReST API
- fixed pulling stats for dhcp6 when there is no dhcp4 daemon

Combined all changes in the migration #12.