Build files written before user can select location

1. Open a CMake-based project.
2. In Projects mode, add a new build configuration.
   As soon as you entered a name for the build configuration, Creator creates a build directory and writes files to it. This happens before the user has a chance to select a different build directory.
   Changing the directory for the new build configuration will only create yet another directory.

I think the build directory should not be created until the user actually triggers a build.