Do not list duplications when searching history

The key 'unique' is introduced in IPython as of:
https://github.com/ipython/ipython/pull/2792
Update changelog
Show recent history first in helm/anything UI
Merge branch 'history-unique'

History search using helm/anything discards duplications.
This functionality requires at least version 4.0 of IPython kernel.
https://github.com/ipython/ipython/pull/2792