Implement MEF to allow for plugin architecture

[vbjay]

Use MEF to allow for a plugin process where other developers generate dlls that get placed in a plugins folder and tasks can be registered through MEF. This will allow dynamic processing of images and allow growth.

Things to deal with to make this happen

• Need to limit how many child tasks run at the same time at each task level
  • Each task generates its children so that a large task can be broken up and result data can be processed further.
  • If too many tasks are yielded at the same time, memory can be an issue along with too many tasks processing at the same time.
  • Using a ConcurrentQueue could help in this
  • Have app.config provide how many tasks get started at once.
• Provide a Producer/Consumer design possibly
• Move Task Definition and FileProcessor classes to a class library and provide plugin interfaces and such