Initial implementation of GTFS support

It is a simple implementation to support public transport and GTFS import. I tested it with Dijkstra and real world data and it works very well.

The ```GTFSReader``` uses GraphStorage to generate a time-expanded graph from a gtfs file. The time is encoded in the graph structure. Therefore, for each station multiple nodes are created which represents the station at a given time. The distance between nodes are the time difference in seconds. 

For GTFS import the onebusaway-gtfs library is used. But trips which uses frequencies.txt are not yet supported.

 ```GHPublicTransit``` is modeled after ```GraphHopper``` and  can be used as high level interface. 
 There is also ```PublicTransitMiniUI``` which can be used to test and debug GTFS files.