E19, E10

Update MenuActivity to adopt MenuItemAdapter
     - Display both name and price of the item now
Update VendorActivity
     - Disable view menu button when no menu item is available
     - View Reviews is now functioning
Add 0 to 5 stars pictures
Add ReadReviewActivity, ReviewAdapter
Add VendorReview object
Update doc
Update Cart and Order .java
Merge pull request #2 from Intuitive/Zeng-Sprint2

Zeng sprint2
added CartActivity, E17, E13
fixed remaining conflicts
Merge pull request #4 from Intuitive/Fifi2

Fifi2
Merge branch 'master' into nik