Improved navigation layout and made it more DRY.

 On branch master
 Your branch is up-to-date with 'origin/master'.

 Changes to be committed:
	modified:   app/models/exzbike.rb
	modified:   app/views/exzbikes/index.html.erb
	modified:   app/views/exzweights/index.html.erb
	modified:   app/views/layouts/application.html.erb
	modified:   app/views/main/index.html.erb