Prompts based on `mkComplFunList` and `mkComplFunList'` were not
taking into account the `searchPredicate` funtion from `XPConfig`.
This was rather confusing.
We fix it by passing `XPConfig` to these functions; although
this is strictly more than they need, it makes the breaking change very
easy to fix and is also more future-proof.
* Previously I was removing empty workspaces after switching away from
them, but this seemed to cause a bug when workspaces were defined
statically in your XMonad configuration.
* Next up: a function to delete an existing project.
