Add pagination to commands collection

The commands collection, which can grow quite lengthy, currently does not
allow any pagination. This provides the "start" and "limit" query arguments,
which are present for many other collections.

app.rb

@@ -560,7 +560,7 @@ def render_template(name)
   # hand-coded list, but ... it will do, for now.
   COLLECTIONS = [:brokers, :repos, :tags, :policies,
                  [:nodes, {'start' => {"type" => "number"}, 'limit' => {"type" => "number"}}],
-                  :tasks, :commands,
+                  :tasks, [:commands, {'start' => {'type' => 'number'}, 'limit' => {'type' => 'number'}}],
                  [:events, {'start' => {"type" => "number"}, 'limit' => {"type" => "number"}}], :hooks]
 
   #
@@ -703,6 +703,8 @@ def paginate(start, limit)
   end
 
   get '/api/collections/commands' do
+    start, limit = paginate(params[:start], params[:limit])
+
     collection_view Razor::Data::Command.order(:submitted_at).order(:id),
       'commands', limit: limit, start: start, facts: true
   end