Add API for Mobile Share window

[idna001]

If youre achive a highscore there is the ability to share the achievement.
By pressing sharing on a mobile device the share Button from the browser should come up.

This is partly done, but not functional

Thanks for contributing

[idna001]

#44

[tchesa]

This is already there. Maybe we can close this.

[idna001]

@tchesa yep, sadly is working on every testcase. Safari shared window don't work yet