Update shipping.php

Added install/uninstall class check similar to modules/payments/etc.
Merge pull request #1159 from OpenCartAddons/patch-1

Update shipping.php
more admin menu bar done
Merge branch 'master' of https://github.com/opencart/opencart
Fix to PayPal Express module - incorrect variable used to search the zone table to try and match the zone name. Fixes 1152
Merge branch 'master' of git@github.com:opencart/opencart.git
finished adding the admin menu code
Merge branch 'master' of https://github.com/opencart/opencart
footer update
work done on the admin notification system
Merge branch 'master' of git@github.com:opencart/opencart.git