Couchbase Cachehandle - updates and open issues

[MichaConrad]

I haven't updated/tested the implementation for Couchbase in a while and found that there are some things missing / not working as expected. They also added support for netstandard1.5, which means I can now finally cross target the package for net45 and netstandard.

• Configuration Features
  • Add support for using ClusterHelper which already handles configuration and such statically
  • Add overload to use already configured ICluster or IBucket?
  • Add support for password protected buckets
  • Add support for the new authentication features which are per cluster
• Update to latest version with netstandard support and multi-target
• Sliding expiration is not always working
• Run all unit tests
• clear region not implemented (use same solution as for pure memcached handle)

[MichaConrad]

done except clear region - can be done later