serveral enhancement

1.make template to generate nav-bar to remove duplication
2.change date propery in expense model to "string" type
3.remove dependency of datejs
4.add "required" and regexp pattern to "amount" field of form
5.make Modernizr.js plain
6.add comment to beginning of main.js to record TODO list
7.implement some of basic db operation (create/drop) under admin tab