Create test data

[dodie]

The application currently needs HGT data from NASA to do anything. (see the readme).

It would be good to have some fake HGT tiles as test data so it could be used as part of an automated test suite to verify calculations and to quickly check how the rendering looks.

A potential solution could be to actually generate the HGT files, or it might be even better to create factory classes that would produce different elevations.