some minor implementations from chapter 11
function 'add' to line item + route
changed function 'remove' in line items + route
added button to '+' to show cart
added button '-' and 'x' to show cart
changed 'add to cart' button
created _cart partial and added to the store view
cart new layout
Merge branch 'master' of https://github.com/meubreake/depot

iteration F1 + styling