Switch all uses of realpath to abspath.
Switch all uses of realpath to abspath.

I only *needed* to switch this in `pjoin` for it to resolve static files
lazily, but I figured it wouldn't hurt to switch all of them and now
they will all behave better with symlinks

jupyter/jupyterlab,jupyter/jupyterlab,jupyter/jupyterlab,jupyter/jupyterlab,jupyter/jupyterlab