Refactor PageContext
Refactor PageContext

Now shows a better error for not-found pages.

urkerab/Pokemon-Showdown,xfix/Pokemon-Showdown,svivian/Pokemon-Showdown,svivian/Pokemon-Showdown,svivian/Pokemon-Showdown,xfix/Pokemon-Showdown,sirDonovan/Pokemon-Showdown,sirDonovan/Pokemon-Showdown,svivian/Pokemon-Showdown,xfix/Pokemon-Showdown,Zarel/Pokemon-Showdown,Zarel/Pokemon-Showdown,xfix/Pokemon-Showdown,urkerab/Pokemon-Showdown,Zarel/Pokemon-Showdown,svivian/Pokemon-Showdown,sirDonovan/Pokemon-Showdown,urkerab/Pokemon-Showdown,xfix/Pokemon-Showdown