package.py: Add preliminary pkgconf support

Add the beginings of keeping data related to packages in config.yaml.

* Split extracted locate_in_devsrc and locate_in_path from locate_locally.
* Removed parents arguments from package objects.
* Added "pkgconf" to PackageData.
* Removed "status" from PackageData, it will now be part of pkgconf.
* Change PackageStatus.status to PackageStatus.tag
* Change PackageStatus.message to PackageStatus.message
* Reordered functions
* Reordered tests