Header is now easier to maintain.

Changed the way links work. Now they are pushed into arrays and
printed later on. Also if loading requires more javascript
files they may be added to header.
Minor cart code realignment.
Username can now be retrieved from user model.
Worker can now see and accept orders.

One way order status changing for worker added.
User may change order status via javascript and
save it to database automatically.
Merge branch 'master' of https://github.com/RobertaM/PSA