SFC-UI added metadata functionality

+ new tab NSH metadata
+ possibility to define context/variable metadata
+ attachment to SFP/ACL is prepared but disabled at the moment
  (because of missing YANG models)

Change-Id: Ief2b7dae731b92d928ee04211a61e14c48e9b316
Signed-off-by: Andrej Kincel <akincel@cisco.com>