IVE: Sync filesystem state with implementations configuration

When user changes the Current there are now 2 cases:

1. work/functionName/language is already a symlink => just delete the symlink and put a new one pointing to the newly selected current
2. work/functionName/language is not a symlink => move it to implem

There will always be only one symlink active at a time (the work/language pointing to the current implementation in work/implem/implementationName/language)