Custom profiles: order of repositories

When creating a custom profile, custom repositories that are added to the profile are always added after the default repos:

```
mavenLocal()
maven { url "https://repo.grails.org/grails/core" }
```

This was not allowing grails applications to pull dependencies in our environment where all dependencies are sourced via Nexus. Our Nexus repositories had to be first in the list in order for these dependencies to be retrieved.