SteemConnect: Login with memo key is now disabled

Hey developers,

Here is a small update to inform you that today we've made a change on SteemConnect for disable login with private memo key. This change has been requested previously mostly because there been a lot of private keys leaking around. Since the release of Byteball bot to reward users for Steem attestations we've preferred to disable login with memo for good to avoid abuses.

Fabien