Switch GoCart to use PHP's built in sessions

CodeIgniter session library was killing some login sessions and
anything added to the session with a backslash was killing it. We
replaced the built in CodeIgniter session class with a custom one to
facilitate all the existing places in the code that referenced it.
Fix admin check to reference the correct library

this changed with the session replacement.
Remove the html_entity_decode due to some some characters getting improper encoding.