Breakpoint Tweaks

- Extra large viewport breakpoint now at 1500px and up. Post thumbnails
in 3 columns + featured posts.
- Large viewport now at 1500px and below. Post thumbnails in 2 columns
+ featured posts.
- Medium and small viewports layout now the same. Post thumbnails in 3
columns, no featured posts.
- Added a bunch of container width overrides using additional media
queries.
- Fixed display bug where glyphicons are not being displayed correctly
on localhost and some icons not being displayed on live server.
- Replaced grey image placeholders with actual images.
- Implemented mobile version of banner on mobile viewport.
- Implemented mobile version of logo on mobile viewport.
- Bunch of layout issue fixes and tweaks.