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 
Change this to:
`$meta = wp_stream_get_meta( $record );`

Because the meta is already in the `$record` object. If you only pass the `ID` to `wp_stream_get_meta` then it does a whole new API call.