WIP: Integrate IPython setup on windows

I tested this on a brand new windows system with nothing but julia installed:

````julia
Pkg.clone("https://github.com/davidanthoff/IJulia.jl.git","IJulia")
Pkg.checkout("IJulia", "integratedipysetup")
Pkg.build("IJulia")

using IJulia
notebook()
````

works on that system.

This PR lacks proper error handling etc, consider it more a proof of concept.
I'd rather re-organize this function to the form
```
function ipython_version(ipython::String)
    convert(VersionNumber, chomp(readall(`$ipython --version`)))
end

function find_ipython()
      for ipy in ("ipython", "ipython2", "ipython3", "ipython.bat", normpath(Pkg.dir("IJulia"),"deps", "usr", "python27", "scripts", "ipython.exe"))
          try
                return (ipy, convert(VersionNumber, chomp(readall(`$ipy --version`))))
          end
      end
      error("IPython is required for IJulia")
end