PDF document processing. Includes:

* Refactor ProcessorFake to be enabled via a boolean config var
* Refactor classes to have more logical names
* Add DocumentProcessorDispatcher
* Create a NullProcessor for unknown files
* Add PdfProcessor, using the "pdf-reader" gem
* Introduce DocumentProcessorDispatcher
reindenting
sorts the annotation list by where they appear in the document
WIP - struggling to get integration specs running...