Issue 612 - Custom connectors contexts removal from post/taxonomy connectors

@fjarrett Please review. And if you can please test woocommerce integration, might need some more work, as I've made it so related post-types/taxonomies records are registered under its connector name.

Resolves #612 
I'm getting a missing argument warning showing up in each record in the list:
`Missing argument 2 for WP_Stream_Connector_Taxonomies::action_links()`