Add class for tab headline
semantic markup in info module

Replace em with h3 to point out meaning.
right align big play button

Replace variable $play-button-margin with $margin-base-horizontal.
generalize styles

Define general vertical and horizontal margins in 2 sizes: base and small.

Set small margins to elements in small screen resolutions and base margin
for default layouts.

Align all elements vertically, depending on screen resolution

Minor font-size and font-weight adjustments.
Merge pull request #199 from podlove/mobile-alignments-and-font-sizes

Mobile alignments and font sizes