enhc Improve section starters

Improves the section starters by making them full responsive, have
differnt breakpoints for mobile.

Other changes:
- Added viewport meta tags to base template to ensure android devices
  correctly render the responsive layout. Found this out while testing.
- Added horizontal and vertical centering code to util which I used.
- Removed the xtra large breakpoint and am just using the large layout.
Merge pull request #62 from msecret/enhc-improve_section_starters

enhc Improve section starters