Add "Getting started" guide

[ksiazkowicz]

It should be easier for user to make a transition from 0.3.1 to 0.4 and make it easier for new users to get around the UI as well.

Guide should appear after First Run wizard. User should be able to skip it, of course.

• show where the contact list is
• show how to get online
• show how to create a new account
• show how to dismiss notifications
• show how to interact with notifications
• let user know they can swipe the chat out of the screen
• explain where received files end up
• etc.