Working draft of KernelHistoryManager
Addressed issues: renamed ZMQHistoryManager (appears to do need to do more than just an Accessor) in IPython/terminal/console/zmqhistory.py; added abc methods; rewrote access methods to load the history from the kernel client; works with 'ipython console' and with 'ipython console --kernel'
Addressed issues: replaced abc with NotImplementedError; removed unneeded methods; fixed typo
ZMQHistoryManager made to work with testing KernelClient which has no history method
Removed unneeded import
Merge pull request #6933 from dsblank/master

`ipython console` requests the history from ZMQ-based kernels