refactor osn to use osmdroid jar

OSN actually use a very old fork of osmdroid source code.
osmdroid project evolves very quicky (thanks to a lot of devs), and now provide a jar library.
Because we forked a long time ago, it's nearly impossible for OSN to get osmdroid updates and also to contribute back.
Refactoring OSN to use osmdroid jar will give OSN a lot of nice updates, and devs won't need to contribute to 2 projects for the same functionnality (I worked twice to add multitouch in osn and then in osmdroid).