make 'preapproved' payments get same access rights as 'complete' payments

This small tweak seems to address what I brought up in [issue #1232 for EDD](https://github.com/easydigitaldownloads/Easy-Digital-Downloads/issues/1232)
remove 'preapproved' getting same access rights as 'complete' payments
use media_buttons action instead of media_buttons_context filter for "Insert Download" button
Merge branch 'master' of github.com:momnt/Easy-Digital-Downloads into momnt-master