Added tabindex to filter field

Based on however I changed the tabindex of the search field so that it goes search field -> filter field & then back to browser default. I dont think we should override the default tabindex of the page too much
Closes #3706

app/views/dashboard/_projects_head.html.haml

@@ -14,7 +14,7 @@
 
   .nav-controls
     = form_tag request.original_url, method: :get, class: 'project-filter-form', id: 'project-filter-form' do |f|
-      = search_field_tag :filter_projects, params[:filter_projects], placeholder: 'Filter by name...', class: 'project-filter-form-field form-control input-short projects-list-filter', spellcheck: false, id: 'project-filter-form-field'
+      = search_field_tag :filter_projects, params[:filter_projects], placeholder: 'Filter by name...', class: 'project-filter-form-field form-control input-short projects-list-filter', spellcheck: false, id: 'project-filter-form-field', tabindex: "2"
     = render 'explore/projects/dropdown'
     - if current_user.can_create_project?
       = link_to new_project_path, class: 'btn btn-new' do

app/views/layouts/_search.html.haml

 .search
   = form_tag search_path, method: :get, class: 'navbar-form pull-left' do |f|
-    = search_field_tag "search", nil, placeholder: 'Search', class: "search-input form-control", spellcheck: false
+    = search_field_tag "search", nil, placeholder: 'Search', class: "search-input form-control", spellcheck: false, tabindex: "1"
     = hidden_field_tag :group_id, @group.try(:id)
     - if @project && @project.persisted?
       = hidden_field_tag :project_id, @project.id