Add JSON serializer

Add JSON serializer to permit extractors to be saved to file
system in a readable format.

#8
Serialize Extractor

Implemented serilaization on Extractor

#8
Delegating Dispose

Setup token to be exposed as a component (code analysis
warning). Addressing cross-thread issue with accessing
extractors from parallel thread when they are living on thread
with list view control.

#11
Get copy of extractors

Grab a copy of extractors rather than a reference to be iterated
later in the wrong thread.

Fixes #11