Fixes for two credentials bugs
One with nonces when not FTP details are not defined in wp-config.php (fixes #45). Another unreported bug which improves how a failed FTP connection would otherwise respond without showing an error message.
#47. Only plugins which have no source, or a source that begins with the .org repo URL are linked. This patch also adds several other helper methods.
Returns false on the WP filter, if the current screen is the TGMPA page. Otherwise returns existing action links. Fixes #48.