drop local target support

The agent object is now only used in remote-servel control context,
making local target irrelevant.
drop useless Scheduler class

As an agent object is only needed in server-control context, a simple
list attribute is enough to store the targets list.
transfer daemonization logic in executable

No need for unix-specific code in agent object.
drop useless conditions

An agent object is always used in background execution context.
pass explicit option to fork
check fatal conditions earlier