Fixed several haml and sass conventions

* `%div` is implicit in haml
* `+` over `@include` in sass (reads cleaner0
* Use `+clearfix` instead of empty div hacks
Removed flip-flopping nav menu in footer

* Unnecessary duplication across views
* Menus that change underneath every click violate most usability guidelines
Removed main content scaffolding duplication across views
Ensured row layout maxed out the available columns
Fixed general bootstrap container, row, and column layout
Bumped up the sponsor image sizes to match Meetup's dimensions
Cleaned up the event listing styles
Cleaned up the summary pane
Added icons to each page heading
Added tooltips to the sponsor logos
Added tooltips to the photos
Realigned organizers list
Subdued copyright in footer
Merge pull request #9 from rubyloco/style-cleanup

Lots of style changes