Don't specify profile-dir for kernels

we are passing `--profile-dir` to non-IPython kernels. This avoids specifying it to *any* kernels, which includes IPython, which may be premature.

It does clean up something in the console frontends, which blended frontend and kernel args. Now the console frontends  no longer need to understand anything about kernel flags, and kernel args can only be passed after `--`, e.g.:

       ipython qtconsole -- --matplotlib inline

       ipython qtconsole --kernel julia -- --some-julia-flag

closes #6626