Support for file backup compression

As I read in the manual urbackup does not support compression at all, only suggest to use filesystems that are able to use some kind of compression.

Please add support for compression and make it configurable (compression ratio, and whether admin want is to compress on the client side or server side).

There are cases when the storing filesystem cannot be changed (mounted through SMB, and on an old nas which only supports ext4 for example) and also when the clients are much more powerful than the server.

Also I just noticed while trying out backing up to a samba share on linux it says:
“err_cannot_create_symbolic_links). Operation not permitted (code: 1)
UrBackup cannot create symbolic links on the backup storage. Your backup storage must support symbolic links in order for UrBackup to work correctly. The UrBackup Server must run as administrative user on Windows (If not you get error code 1314). Note: As of 2016-05-07 samba (which is used by many Linux based NAS operating systems for Windows file sharing) has not implemented the necessary functionality to support symbolic link creation from Windows (With this you get error code 4390).”

That means deduplication cannot work, since smb does not support hard links. So this case would also benefit a lot from compression.