Make unlimitedfs extract list of scripts/plugins from server.cfg

Previously it was loading ALL plugins and filterscripts found
in corresponding directories. Now it reads the names of filterscripts
and plugins to be loaded from server.cfg, using these optiosn:

filterscripts2 <fs1> <fs2> ....
plugins2 ...
Add RCON command support for unlimitedfs

The new commands are:
 loadfs2 - load a filterscript, same as loadfs
 unloadfs2 - unload a filterscript, same as unloadfs
 reloadfs2 - reload a filterscript, same as reloadfs
Fix OnFilterScriptExit being never called
Fix filterscripts not being unloaded on server exit