Merge pull request #1898 from sumobi/master

fix: PHP warning when remove items from cart when discount is applied on...
Don't set mode by default on EDD_Payment_Query. #1899
Don't load sessions in the admin. #1899
ONly load pages into settings when on the settings screen. #1899
Check truthiness of DOING_AJAX

Don't let wp-config.php or plugins make a liar out of you.
Merge pull request #1900 from JustinSainton/patch-8

Check truthiness of DOING_AJAX
Update plugin updater class
Merge branch 'master' of github.com:easydigitaldownloads/Easy-Digital-Downloads
Use $item instead of $item['id'] in edd_email_receipt_download_title