Deprecate expanding task and related

[joeha480]

ExpandingTask was introduced to solve an identification problem before the identity package was created. Now that the input file can be identified properly before starting the task system, it's perhaps not needed anymore. Corresponding methods in the tasks package also need to be deprecated, for example: ReadWriteTask execute(File input, File output)

[joeha480]

While this might not be strictly required so support known implementations, it is still a useful feature. It should however be used with care, since it can have a negative impact on user experience.