Modular plugin system

[AaronHolbrook]

Along the lines of Easy Digital Downloads or WooCommerce's plugin to a plugin system, we should build a system that allows us to modularize things like 'related posts', 'Buddypress searching', 'admin search' (although this one we might want to include in core by default).

[AaronHolbrook]

I think this will need to be done on a case by case basis and will primarily rely on hooks and filters.