Popup improvements

[pheyvaer]

• When hitting "enter", log in.
• After successfully logging in, show message (besides icon).
• When already logged in and open popup, show message that already logged in.
• Log out button.
• Show error when log in fails.

You can split them up in different issues when start tackling them.

[pheyvaer]

Considering the message in your last commit, can we close this issue?