Removed openpyexcel from fabfile
Implemented custom ExtractPluginManager based on the standard Yapsy PluginManager.
Added template JSON ExtractionPluginManager configuration file
Updated plugin constructor arguments handling code
Updated Extract CLI script to use ExtractionPluginManager
Cause ExtractionPluginManager to always append it's own set of plugins
Added ability to explicitly exclude plugins using configuration file
Added skeleton for SQLAlchemyFlatStorage Plugin