launch_daemon: Jobs were started before their target.

* A job must not be launched when its target hasn't been launched
yet. This fixes Tracker launching when the mount_server scanned
the initial disk, even though the FirstBootPrompt was showing.
* Jobs are no longer initialized when their target has not been launched
yet. This also means that you cannot talk to a service beforehand in
this case.
* Slight refactoring and clarifying, even added some documentation :-)
* _TriggerJob() is now called _LaunchJob(), and does all the checks for
jobs that _LaunchJobs() does now for targets.

launch_daemon: Added basic support for conditions.

* Admittedly not very well thought out, but it should be good
enough for now; it doesn't really make sense to initialize jobs
that is never run due to failed conditions.
* Job, and Target now have a common base class BaseJob that deals
with the conditions.

launch_daemon: Moved Job+Target into separate files.

launch_daemon: Jobs were started before their target.

* A job must not be launched when its target hasn't been launched
yet. This fixes Tracker launching when the mount_server scanned
the initial disk, even though the FirstBootPrompt was showing.
* Jobs are no longer initialized when their target has not been launched
yet. This also means that you cannot talk to a service beforehand in
this case.
* Slight refactoring and clarifying, even added some documentation :-)
* _TriggerJob() is now called _LaunchJob(), and does all the checks for
jobs that _LaunchJobs() does now for targets.

launch_daemon: Added basic support for conditions.

* Admittedly not very well thought out, but it should be good
enough for now; it doesn't really make sense to initialize jobs
that is never run due to failed conditions.
* Job, and Target now have a common base class BaseJob that deals
with the conditions.

launch_daemon: Moved Job+Target into separate files.