Require contest durations, prefill end times for unfinished puzzles & allow to modify them

app/controllers/contests_controller.rb

@@ -57,6 +57,7 @@ class ContestsController < ApplicationController
 
     @contest = Contest.new
     @title = I18n.t("contests.new.title")
+    @nonav = true
   end
 
   def create
@@ -69,6 +70,8 @@ class ContestsController < ApplicationController
     if @contest.save
       redirect_to "/contests/#{@contest.id}/settings/general", notice: t("contests.new.notice")
     else
+      @title = I18n.t("contests.new.title")
+      @nonav = true
       render :new, status: :unprocessable_entity
     end
   end
@@ -203,7 +206,7 @@ class ContestsController < ApplicationController
   end
 
   def new_contest_params
-    params.expect(contest: [ :name ])
+    params.expect(contest: [ :name, :duration ])
   end
 
   def settings_general_params