dismissible minimum browser banner, closes #CNVS-5043

dismisses the banner for the browser session

test plan:
- use canvas in an unsupported browser (e.g. ie8, old firefox,
  or set your user agent to an unsupported one)
- click the minimum browser warning at the top of the page
- the warning should be dismissed
- when visiting other canvas pages the warning should still be dismissed
- restart the browser
- the warning should be visible again

Change-Id: I0d8bc966e8512e07dab0448f68a538a256228c4e
Reviewed-on: https://gerrit.instructure.com/19623
Reviewed-by: Jon Jensen <jon@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Joe Tanner <joe@instructure.com>
QA-Review: Joe Tanner <joe@instructure.com>

app/coffeescripts/jquery.rails_flash_notifications.coffee

@@ -4,6 +4,7 @@ define [
   'underscore'
   'compiled/fn/preventDefault'
   'jqueryui/effects/drop'
+  'vendor/jquery.cookie'
 ], (I18n, _, preventDefault) ->
 
   $buffer = $("#flash_message_buffer")
@@ -12,6 +13,7 @@ define [
   $holder.on 'click', 'li', ->
     $this = $(this)
     return if $this.hasClass('no_close')
+    $.cookie('unsupported_browser_dismissed', '1') if $this.hasClass('unsupported_browser')
     $this.stop(true, true).remove()
     if (bufferIndex = $this.data('buffer-index'))?
       $buffer.find("[data-buffer-index=#{bufferIndex}]").remove()

app/controllers/application_controller.rb

@@ -1369,7 +1369,9 @@ class ApplicationController < ActionController::Base
   def flash_notices
     @notices ||= begin
       notices = []
-      notices << {:type => 'warning', :content => unsupported_browser, :classes => 'no_close'} if !browser_supported? && !@embedded_view
+      if !browser_supported? && !@embedded_view && !cookies['unsupported_browser_dismissed']
+        notices << {:type => 'warning', :content => unsupported_browser, :classes => 'unsupported_browser'} 
+      end
       if error = flash.delete(:error)
         notices << {:type => 'error', :content => error}
       end