Fixed issues with time zones and new html5 apis (#12783, #12784)

 * Switched to use datetime-local instead of dropped datetime input type
 * Switched to use str representation of dates during communication to
   get rid of timezone issues. Now server side time zone should be
   respected.
 
Change-Id: I9793e30c669e5367fcf3864b9f097e3bf15947fb