Possibility to take elevation data into account

This pull request adds elevation data to GraphHopper. Please have a look and report back any issues you get or you see!

Several things were necessary to do so:

 * several data structure needed an elevation property
 * the import process needs to import elevation data, we currently use SRTM but others like CGIAR will follow
 * If a special FlagEncoder is used there are two speed values (up and down hill). Useful for traffic jams too. This is already merged to master. See Bike2FlagEncoder for an example.
 * The UI now displays the elevation nicely per route if imported, see below

The master branch already has cherry picked some changes from this:
 * the introduced reverse property in e.g. the Weighting.calcWeight method
 * the algorithms now have a notion of two weights per edge
 * CH is working for two weights per edge

There are still some things to do:
 * speed up of several things
 * the web API should be moved to #164 in order to avoid "clear text" coordinates for instructions which is especially bad for biking & hiking tours
 * trying out world wide coverage and preparation
 * currently not possible to use elevation only for speed changes and throw away after import

![ele-screenshot](https://f.cloud.github.com/assets/129644/2450114/4b10626e-aeb8-11e3-8db0-810884318d23.png)