These messages are used by console frontends to check whether the
current input is complete or not. If it is not complete, the next line
is treated as the continuation of the code, and a '...' prompt is used
to show that.

To provide support for qtconsole, I have made it such that IHaskell
always responds to an is_complete_request by saying that the code is
complete, which only allows for single line inputs.

- Make hlint happy.
- Reformat using hindent.
- Add explanatory comments in some places.
- Use Control.Monad.foldM for IHaskell.Eval.Widgets.widgetHandler

It just works.

Separate out publish to IHaskell.Publish
Replace publish with publishResult, which also requires more arguments.

Previously, the kernel would die when opening a notebook with widgets
as there is no widget stored in the kernel when it starts.

Evaluate accumulated widget messages in the Ghc Monad, after a comm_msg
recieved from the frontend is handled.

- Move dupHeader to IHaskell.Types
- Move handleMessage and widgetHandler to IHaskell.Eval.Widgets
- Make handleMessage and widgetHandler more flexible

Still no visible outputs.