fixed utc/local time convertion bug

1. move the search of Node from FinderSteven.java to Controller
    (In need of conversion of the local time of the airport)

2. change function signature for Controller.search() method
    start and end parameters are now in type String
     (should not be a big deal since it was called by the spring framework)

3. Add conversion of local to UTC time in Controller.java
    
Since Keith said that the time input from users were indicating the local time of the airport(either departing airport or arriving airport, depends on IsOrigin), So I convert the local time to UTC time before pass them to the search engine.

   When the FinderSteven.find is called by the Controller, the start and and parameters are indicating the UTC time.