Icons for the user levels
Merge branch 'master' of github.com:thegooddata/extension

Conflicts:
	chrome/images/apprentice.png
	chrome/images/collaborator.png
	chrome/images/expert.png
	chrome/images/journeyman.png
* Tooltip behavior fixed. Now the tooltip vanishes when the mouse leaves the "share" button and doesn't hover the tooltip.
* The "remember me" and "forgot password" links look the way they should.
* The sign-in button icon is the on-off switch and the text "sign in" appears when the mouse pointer enters the button.