Add more sign-in options

[StorytellerCZ]

Would be nice to have more sign-in options. I think at least:

• Facebook
• LinkedIn
• Meteor accounts

[Ketcap]

Right now this application's audience is developer right now twitter and . github that we wanted but maybe in future we will consider other options :) 👍

[StorytellerCZ]

I think LinkedIn falls into that category as well. 😉