Resolve relative script paths in knut.json

[LeonMatthesKDAB]

It could be quite useful to commit the knut.json into a project, e.g. if the project contains a directory tools/knut-scripts, I would want to add that path to the knut.json.

However, if I do so, at the moment it doesn't actually add it to the script paths.
It works if I add it manually over the UI, but then the fully resolved path is added, which of course differs between machines/users.