* test must check different directories on install/uninstall
* alter uninstall of config to disable the `contrib_nbextensions_help_item/main` nbextension regardless of whether it's installed or not
* Make `user` default to `False`, as otherwise it conflicts with other custom install options like `nbextensions_dir` and `prefix`. This makes app default to system install.
* alter tests to account for new default install
* alter tests to check *all* potential installation directories, to ensure we don't place anything in a location we shouldn't touch
* test app `--prefix=` cli arg
Josh Barnes