Fake symlink support on file systems not supporting symlinks

[nlmarco]

If the destination repository resides on a file system not supporting symlinks, we should not fail, but fake a symlink by using ordinary files (or directories) and locally keeping them in-sync.

CloudStore should create both files (or directories) as real files (or directories) - the real file and the symlink pointing to it - and whenever one is modified the other should be updated locally, before synchronising to/from a remote repository.

If there is a local collision, the normal collision handling should happen (just like it is done when syncing remotely).