Merge pull request #26 from dergraf/master

Tooltip
Minor css changes

background of teaser class changed, image size adjusted
Twitter embed markup added to tooltip

changes to design a bit, but doesn't achieve the desired tweet design.
also: delivers a typeerror every time a tooltip is activated.
Changed .img to .media

related to #18, making things a bit clearer in the code
Work continued on issue #18

Two tasks remaining:
* resize multimedia elements to fit into the .media class
* find out why "read on" links are broken if else if statement is
commented in
Economist link fixed
Open links in a new tab
Issue #18: Distinguish link types to make audio and video playable in the grid
enabled scroll-loader
merged