Implemented Login/security update + Post function

-Users can now sign up and login
-Updated security so that if you are not logged in, it will show a the accessDenied template instead of postsTemplate
-Added a if currentUser statement to the url so that people who are not logged in can't go to that url (header.html)
-Moved the contents in loading.html to header.html(header template) and added inclusion in loading.html
-Users can now submit a post through the form on '/submit' All necessary routing functions were added.