This fix is only a halfway-fix. If there are multiple IHaskell libraries
installed, you can still end up loading an interpreted version of the
wrong one; however, now Display values are serialized to bytestring, so
this will not cause any issues with transferring those between the two
versions. Widget messages are not serializable and cannot be
serializable, so those remain a problem, but instead of crashing it will
instead emit a loud warning on stderr.

This should make the build faster and more reliable,
and hopefully ressurect the test suite.

Also, add some utilities for working with IHaskell components in `stack
ghci`.

The ihaskell-basic display package has been with us for a while, but
has no useful instances and really doesn't help anyone. We're removing
it for the time being but could get it back someday if needed.

Previously, `cabal install ihaskell` would happily use ipython-kernel-0.8.3, resulting in error

    ‘protocolVersion’ is not a (visible) field of constructor ‘KernelInfoReply’

adjust for changes in Caskroom