Add command option to control enable/disable local storage

issue link:http://code.google.com/p/phantomjs/issues/detail?id=1055
Sometimes we need the ability to control whether to enable the local storage or not, especially when we want to build a large scraping system.

Add AppCache, IndexedDb, LocalStorage command line control flags respectively.
Still need to add a global flag to enable/disable the whole disk written actions.