Improve explore proojects page

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/views/explore/projects/_filter.html.haml

@@ -3,7 +3,7 @@
     .form-group
       = search_field_tag :search, params[:search], placeholder: "Filter by name", class: "form-control search-text-input", id: "projects_search"
     .form-group
-      = button_tag 'Search', class: "btn btn-primary wide"
+      = button_tag 'Search', class: "btn btn-success"
 
 .pull-right.hidden-sm.hidden-xs
   - if current_user

app/views/explore/projects/index.html.haml

 - page_title "Projects"
 - if current_user
   = render 'dashboard/projects_head'
-.clearfix
+.gray-content-block.clearfix
   = render 'filter'
-%br
 = render 'projects', projects: @projects
 = paginate @projects, theme: "gitlab"