Cookie approval policy

Cookie approval policy 
(https://www.pivotaltracker.com/story/show/56438038)
- Implemented: https://github.com/peter-murach/rack-policy
- Updated `application.html.erb` to display an alert if user have not previously approved the cookie policy. Alert is displayes on every page as long as user does not click "Close".
- We set a cookie for 1 year to mark that the policy has been accepted by the user

Also in this PR
- Restyled the navbar
- Wrapped the page in a container with a light grey background
- restyled the footer to stick to the bottom of the page
- fixed some format issues on `organizations/show.html.erb`