Adds the capability for the HandBrake and Bluray source plugins to look
for sources in multiple directories using the new features of the config
class to support string lists.
Moved common default init/name methods to a base class, common to all
plugin types.
Added phpdoc comments to various plugin methods.
Updated HandBrake plugins to reflect core changes.
A job may remain in the database after the source dir has been deleted.
The source object has been changed to permit construction even if the
source it represents doesn't exist, but will throw an exception if any
requests are made of the object.
