Added symlink support.

Added symlink support:
1. Monitoring symlinks
2. Loading symlinks from content data file

New content data file format:
  number of contents
  content1
  content2
  ..
  number of instances
  instance1
  instance2
  ..
  number of symlinks
  symlink1
  symlink2
  ..

Where symlink format is:
  server, symlink path, symlink target