Allow subcommand arrays in remctl::server::command class

As suggested by @rra, subcommand arrays like:
```
command subcommand1 /usr/sbin/command logmask=3,4 \
    ANYUSER
command subcommand2 /usr/sbin/command logmask=3,4 \
    file:/etc/remctl/acl/myaclfile
[...]
```

should be possible.

The mandatory parameter `command` of `remctl::server::command` class now allows it.
Fix logical issue in port management

* As pointed out by Russ A., when user was specifying a non standard port
for remctl server, file `/etc/services` was updated which is non wanted.
If a non standard port is specified, xinetd service type UNLISTED is used.

* As Russ A. said, UDP protocol is very unlikely to be used so UDP declaration
in `/etc/services` was removed
Split server and client manifests

* As suggested by Russ A., a class `remctl::client` was introduced
to handle remctl client installation.
* Class `remctl::server` now manages remctl server installation
* Class `remctl` now does nothing and should not be used anymore