* get the converted post id with the 'go_subscriptions_converted_post_id' filter
* removed the restriction that only go-subscriptions can set read_post and read user caps
changed the 'go_subscriptions_converted_post_id' filter to 'go_subscriptions_thankyoucta' to customize the button cta on the thank you page.
Merge pull request #23 from wluo/freebird-v2

get the converted post id with the 'go_subscriptions_converted_post_id' filter